Game of Thrones prequel projects

HBO is developing multiple prequel projects to follow the main Game of Thrones TV series.

As of June 2018, four different pitch ideas are being considered, by four separate potential showrunners. David Benioff and D.B. Weiss will not return to write for subsequent projects. George R.R. Martin has seen the pitch ideas and will personally be a co-producer on two of them.

Martin has insisted that these upcoming projects be called "successor shows" or prequel projects, but not "spinoffs" - feeling that "spinoff" implies a deeper connection to the Game of Thrones TV series, but any potential ideas they are considering take place generations or centuries before the main TV series, and would not feature living characters or returning actors. Martin has also confirmed that they are not considering any sequels set after the main Game of Thrones TV series.

Origins
On May 4th, 2017, HBO announced it had ordered pitch scripts for five separate Game of Thrones prequel projects. While the identity of each prequel was not revealed, the five potential showrunners were announced as:


 * Jane Goldman
 * Max Borenstein
 * Brian Helgeland
 * Carly Wray
 * Bryan Cogman

David Benioff and D.B. Weiss do not intend to be involved in the prequel projects, though they technically remain attached as executive producers due to owning the production rights.

George R.R. Martin subsequently made an extensive post on his personal blog about the announcement. Martin confirmed that while at the time, HBO announced only four prequel pitches, a fifth had also just been presented, but for some reason wasn't included in HBO's announcement. It was only confirmed four months later, on September 20th, that the fifth prequel pitch was being developed by Bryan Cogman.

Martin explained in his blog that he first discussed making prequel series with HBO in August 2016 (after Season 6 of the main series finished airing). At the time, he pitched two prequel ideas: one of these continued as one of the announced set of five ideas (it is unclear which one), while the other idea was rejected and never made it that far.

The only clue Martin gave in 2017 about the identities of the five prequel pitch ideas was that one of them was not "set in Westeros" - though whether he meant it didn't take place in Westeros at all, or had parallel storylines in Westeros and Essos, is unclear (i.e. Daenerys Targaryen's storyline in Season 1 isn't "in Westeros" but that season does not exclude Westeros, with other characters). Martin also gave two other brief pieces of information, confirming that none of the ideas being pitched is a sequel to the main series (considering that the main novels aren't even finished yet) but prequels, and will not include any living characters from the main series. Moreover, he officially ruled out a few prequel ideas (see section below). As Martin said:


 * "Every one of the concepts under discussion is a prequel, rather than a sequel. Some may not even be set on Westeros. Rather than 'spinoff' or 'prequel,' however, I prefer the term 'successor show.' That's what I've been calling them."

Jane Goldman and Carly Wray's projects both have George R.R. Martin himself attached as a co-producer, though he has had ongoing story discussions with every showrunner:


 * "It was stated in some of the reports that I am working with two of the four writers. That's not quite right. I've actually been working with all four of the writers. Every one of the four has visited me here in Santa Fe, some of them more than once, and we've spent days together discussing their ideas, the history of Westeros and the world beyond, and sundry details found only in The World of Ice & Fire and The Lands of Ice & Fire...They are all amazing talents, and I am excited to be working with them. In between visits, I've been in touch with them by phone, text, and email, and I expect there will be a lot more back-and-forth as we move forward."

HBO executives have said that, due to the massive logistics involved, only one of these projects will be produced as a full TV series at any one time. HBO representatives have repeatedly stated that they don't intend for the first prequel to air immediately after the Game of Thrones series finale (in the sense that it won't premiere the same night as the series finale, a promotional style other franchises have followed in the past). Martin believes that HBO is aiming for the first one to premiere in 2020, one year after the Game of Thrones series finale.

It is unknown if all five pitch ideas are even meant to be full "TV series" lasting in the range of 4-5 TV seasons, or take the form of a one-shot miniseries, a high-budget TV movie, etc. If one of them is a one-shot special, not a full TV series, it's possible that it might go into production alongside one selected as the main "ongoing full TV series" - depending on its scale and format - but nothing is established yet.

Pilot orders
On June 8th, 2018, HBO announced that it has ordered a live-action pilot episode for Jane Goldman's prequel pitch, and revealed its identity: it will be about the Age of Heroes and the Long Night that occurred during it, when the White Walkers first appeared and nearly destroyed the world.

On June 11th, 2018, George R.R. Martin made a post on his personal blog to congratulate Goldman, and give an update on the current status of the prequels:


 * As Martin had implied in an earlier blog post, one of the five pitch ideas has been rejected (though he didn't identify which one).
 * It is unknown why Cogman's pitch was announced later than the other four in 2017 - it is unclear if this indicates that HBO wasn't as confident in it, which would imply that it was the idea which was dropped. It is equally possible, however, that one of the other four pitches is the one that was dropped (Cogman's pitch may have taken four months to confirm simply due to background contract and scheduling negotiations).
 * Goldman's project has been ordered to pilot, but this is no guarantee that it will be a full series pickup (considering that even the original Pilot episode for Game of Thrones itself was rejected, and the project nearly cancelled afterwards).
 * The three remaining prequel pitches are still in active development. Goldman's pilot has by no means been settled upon as the finalist. HBO has given Martin the impression that at least one, and possibly all three, of the remaining pitches will actually get orders for pilot episodes of their own. HBO will then apparently choose which idea to order a full series for based on the strength of these two-to-four pilots.

The Long Night


On June 8, 2018, HBO put out a press release that it had ordered a pilot episode for the prequel pitch by Jane Goldman - with George R.R. Martin attached as a co-producer. It provided this short description for the prequel:
 * "Taking place thousands of years before the events of Game of Thrones, the series chronicles the world's descent from the golden Age of Heroes into its darkest hour. And only one thing is for sure: from the horrifying secrets of Westeros's history to the true origin of the White Walkers, the mysteries of the East, to the Starks of legend...it's not the story we think we know."

The White Walkers first attacked during the Long Night, which occurred some 8,000 years before the War of the Five Kings and narrative of the main series, during a historical epoch known as the Age of Heroes.

On June 11th, 2018, George R.R. Martin commented on the announcement in his personal blog. He said that he personally thinks this prequel should be titled "The Long Night", but he doesn't have final say - and he suspects HBO will probably put the words "Game of Thrones" in it too so audiences know it's a related project ("Game of Thrones: The Long Night", "The Long Night- A Game of Thrones Story", etc.).

Naomi Watts will portray the lead character in the series, described as "a charismatic socialite hiding a dark secret". Josh Whitehouse will also star in the series.

Untitled Carly Wray prequel pitch
Another prequel pitch was made by Carly Wray, its identity still unknown.

Untitled Brian Helgeland prequel pitch
Another prequel pitch was made by Brian Helgeland, its identity still unknown.

Untitled Max Borenstein prequel pitch
Another prequel pitch was made by Max Borenstein, its identity still unknown.

Untitled Bryan Cogman prequel pitch
Another prequel pitch was made by Bryan Cogman, its identity still unknown.

For some reason, though Martin said Cogman was working on it in May 2017 alongside the other four pitches, it was only formally announced a few months later in September 2017 (possibly just due to scheduling, see above).

Officially ruled-out prequels
Of the five prequel projects being considered by 2018, Martin did rule out certain prequel ideas which are definitely not among them:


 * Robert's Rebellion - Martin confirmed this is not among the five pitch ideas, and he reiterated that he never wants it to be adapted as a live-action prequel. Even before the Game of Thrones TV series, Martin has consistently said that he never wants to even write a prequel novella detailing Robert's Rebellion through active POV narration. Robert's Rebellion is a framing device for the main A Song of Ice and Fire series, and as the novels progress, more and more of its events are revealed through flashback - to the point that Martin feels he will have revealed everything about it by the time the main novels end (moreover, Robert's Rebellion only lasted one year in-universe, and probably could not sustain a TV show lasting multiple seasons - at most, a miniseries or TV movie, but Martin doesn't want it adapted at all).
 * The Tales of Dunk and Egg - Martin stated that this is not among the five pitches, and while he does want to see it have a live-action adaptation at some point, he only wants to do so after the prequel novella series is finished. The main Game of Thrones TV series went into production before the main novel series was finished, leading to numerous complications. In turn, he has also said he won't finish the Tales of Dunk and Egg until the main novel series is finished. So far, this prequel series consists of three novellas, out of a planned ten to twelve. In Martin's own words: "We're not doing Dunk & Egg...I don't want to repeat what happened with Game of Thrones itself, where the show gets ahead of the books. When the day comes that I've finished telling all my tales of Dunk & Egg, then we'll do a tv show about them... but that day is still a long ways off.
 * The reign of Aegon the Unworthy - Since the late 1990's, Martin has actually said that he might enjoy writing a prequel novel about the reign of Aegon IV Targaryen - infamously the worst king in the history of Westeros. Tonally, he described the story as somewhat in the style of Blackadder or Flashman, with a villain protagonist who cheats his way to power. Nonetheless, Martin mentioned in comments on his blog that Aegon the Unworthy is not one of the five prequel pitches currently being considered.

Potential identities of the prequel pitches
There are several distinct prequel eras in the backstory of the main A Song of Ice and Fire novels - many of which were further rounded out by The World of Ice and Fire sourcebook released in 2014. While writing the World book, Martin developed far more material for these prequel eras than could be published in it. He later released sample chapters from his notes as prequel novellas: The Princess and the Queen (2013), The Rogue Prince (2014), and The Sons of the Dragon (2017). Martin later decided to collect all of his currently existing but unpublished notes together into another sourcebook, Fire & Blood (2018), which focuses on the first half of the reign of the 300 year reign of the Targaryen dynasty. Fire & Blood will incorporate and expand upon the previously released sample novellas.

It is possible that HBO is considering pitches for these previously established, distinct prequel eras, given that Martin already developed a considerable amount of material for them. On the other hand, the first prequel pitch that HBO ordered a pilot for was The Long Night - which has no prequel novellas associated with it, and hardly any information at all, as it was a legendary event thousands of years before the main novels which is shrouded in myth.

The Game of Thrones TV series has actually "adapted" some of these prequel novellas in some form before, for the animated Histories & Lore Blu-ray featurette series. For Season 5, HBO made the unprecedented step of putting out a special super-sized 20 minute animated special on the Dance of the Dragons, and then for Season 7, released a 40 minute animated special on the Targaryen Conquest, "Conquest &amp; Rebellion". These may well have been attempts to seed interest among casual viewers of the main TV series in these two major prequel eras - HBO even gave these animated featurettes special screenings in select major cities.

In late July 2017, Elio Garcia and Linda Antonsson, who run the major book fansite Westeros.org, made a set of videos speculating on the identity of the five prequel pitches. They co-wrote The World of Ice & Fire with Martin and have had a close relationship with him for years, and based their speculation on what prequel ideas could plausibly sustain a TV series, while taking into account that HBO will probably want them to be topics that casual viewers of Game of Thrones would be able to recognize. They believe that the most likely prequel pitches HBO would be interested in are the Targaryen Conquest and the Dance of the Dragons.

Going through the Timeline of major events in the history of Westeros and the lands beyond it, Elio & Linda gave an assessment for which distinct prequel eras exist, and which could plausibly be adapted as a TV series. This only covers pre-existing stories within the legendarium that HBO might adapt, and doesn't cover the possibility that HBO might invent a new story that plausibly could have happened in the 12,000 year long history of Westeros (i.e. wars between the independent Seven Kingdoms after the Andal Invasion but before the Targaryen Conquest wouldn't "contradict" anything from the novels, while still being TV-invented content). Elio & Linda split the possibilities into two groups: prequel ideas set (primarily) in Westeros, and prequel ideas set beyond Westeros.

Potential prequels set in Westeros

 * The Long Night - When the White Walkers first attacked 8,000 years ago, and the Wall was built.
 * Elio & Linda actually didn't think this could easily be televised, because Martin never gave an extensive narrative about it. While "fighting the White Walkers" is a fairly linear narrative, other parts of the Age of Heroes are more episodic and difficult to combine (unless in an anthology format).
 * On the other hand, the Long Night actually has very strong name recognition among casual viewers of the original TV series who didn't read the books, one of the major criteria they felt were important. Given that the main looming threat of the narrative is the return of the White Walkers, their original attack is frequently mentioned - more than the Dance of the Dragons, and arguably as much or more than the specific details of the Targaryen Conquest. As it turned out, this was the first prequel pilot ordered into production (to the surprise of Elio & Linda). The only hint that Jane Goldman gave about her prequel beforehand was, indeed, that it was a name that people who only watched the TV series would still be able to recognize as an event in their history.
 * The Andal Invasion - When the second large human ethnic group migrated to Westeros 6,000 years ago - the Andals, conquering and merging with the First Men. They brought with them the Faith of the Seven and traditions of Knighthood.
 * Elio & Linda were dismissive about adapting this as anything but a series of anthology stories, as it is even less connected and with some stories taking place centuries apart. The Andal invasions have also been mentioned less prominently in the main TV series than the Long Night, so a casual audience wouldn't be as attracted to them. They did not seriously think HBO is considering this.
 * The Targaryen Conquest - Taking place 300 years before the main TV series, when House Targaryen conquered and unified the Seven Kingdoms of Westeros for the first time in history, due to possessing the last three living Dragons in the world. Centering around Aegon I Targaryen, and his sister-queens Visenya and Rhaenys, showing them conquer Westeros, forge the Iron Throne, and build King's Landing.
 * Elio & Linda very firmly considered this to be one of the prequel pitches HBO ordered, possibly the most certain of all. It strongly matches all of the criteria: Martin actually did write prequel novellas about this era so there is pre-established narrative to "adapt"; casual viewers of the main TV series would be able to recognize it because it has been mentioned quite prominently throughout the run of the TV series - everyone is fighting over the Iron Throne that the Conquest-generation forged in the first place. Aegon I, Rhaenys, and Visenya have all been mentioned by name in the live-action TV series itself (i.e. Arya and Tywin discuss each of them in Season 2, and how they burned Harrenhal). The storyline would also be fairly linear: diverse enough to be interesting, but not spread across multiple generations like the Andal Invasions, or a sprawling story on the scale of Game of Thrones spanning parallel storylines on multiple continents.
 * The Sons of the Dragon & the Faith Militant uprising - A Cain-and-Abel story of Aegon I's two sons who followed him on the throne: the weakling Aenys and the brutal tyrant Maegor the Cruel. How Maegor warred against the Faith Militant to cement the rule of the new Targaryen dynasty, but then how Maegor's wanton brutality led to civil wars against him. After Maegor died, Aenys's surviving son Jaehaerys ascended to the throne, beginning a golden age of peace that lasted 80 years.
 * Elio & Linda felt this was a good narrative, as Martin had written a prequel novella about it, but it has barely been mentioned in the main TV series - and much more importantly, it is too much of a direct sequel to the Targaryen Conquest to function as a stand-alone prequel. Maegor's mother Visenya is still alive throughout all of these events (still riding a dragon to war at 80 years old). Elio & Linda concluded that this probably wasn't one of the five pitch ideas HBO ordered, but that the Targaryen Conquest pitch probably included notes that if that series extended into 4 to 6 seasons, it would keep going directly into the Sons of the Dragon era. Indeed, the "Conquest & Rebellion" 40 minute animated featurette that HBO produced for the Season 7 Blu-ray set actually extends into the Sons of the Dragon era, including the First Dornish War and mentioning Maegor.
 * Of all the prequel novellas written as in-universe history book outlines, the Sons of the Dragon is the only one for which Martin gave an estimate of how many full books it would sustain if ever narrativized: he has no intention of ever writing it out as books, but he estimated that it could sustain about three novels, functioning as act-breaks within the story (i.e. the reign of Aenys, the rise of Maegor, then the fall of Maegor). The original TV series generally tried to match the natural act structure of the story, with roughly one book sustaining one TV season. Thus if a "Targaryen Conquest" series lasted perhaps 2 or 3 TV seasons, the Sons of the Dragon would take up seasons 4 to 6 or so: thus, combined, they can sustain a full-length TV series of around 6 to 7 TV seasons.
 * The Dance of the Dragons - a massive civil war fought within two rival branches of House Targaryen, one led by Rhaenyra Targaryen and the other by her half-brother Aegon II Targaryen - both the grandchildren of Jaehaerys (making them the grandchildren of Aegon I's grandchildren). The war occurred about 130 years after the initial Targaryen Conquest, and 170 years before the War of the Five Kings. It was the most devastating war in the history of Westeros, as it was the only one before or since in which both sides had dragons.
 * Elio & Linda also very strongly felt that this would make a great prequel TV series, and must be one of the five pitches HBO ordered. They felt that it is tonally the most similar to the original Game of Thrones TV series, with the rivalry between Rhaenyra's faction and Aegon II's faction (the "Blacks" and the "Greens") mirroring the easy to follow Stark/Lannister rivalry from the War of the Five Kings (in contrast, the Conquest is actually about the Targaryens fighting seven different independent kingdoms). Martin also wrote extensive prequel novellas about the Dance, with much more material than on the Conquest (the prequel novella on the Conquest was 10,000 words long, the unpublished notes on the Dance were 60,000 words long). The original TV series also seemed to be attempting to promote the Dance to casual viewers, starting in Season 5 - not only with the 20 minute animated featurette that year, but when Shireen Baratheon gave a long tangent explaining she was reading a history book about the Dance and briefly summarizing what it was.
 * Challenges they felt a live-action Dance of the Dragons would face are its scope and budget. It isn't as widespread as the main A Song of Ice and Fire series, with Daenerys's storylines in the eastern continent, nor does it feature the Wall & the Night's Watch at all - though the Free Cities play a bit larger role (both sides hire mercenary armies from rival Free Cities, but they come to Westeros, instead of the narrative focusing there). There are still more characters and sub-factions involved than in the Conquest, but no more than in the early seasons of the original TV series.
 * What Elio & Linda felt the main issue was is that there were twenty living dragons during this time period, and the CGI budget would be extensive. Elio still felt this was workable, pointing out that 1 - no more than three dragons actually appear in a single battle at any given time (all 20 are never on screen at once), and 2 - the dragons would be the central focus of all the CGI budget, which in the original TV series was divided among other CGI creations such as the armies of the undead at the Wall, or the sweeping vistas of the pyramids in Meereen. Any CGI budget that went to the Direwolves in the original series would also exclusively go to the dragons in this (and CGI dragons are much easier to work with than the fickle actor-wolves who portrayed the direwolves, who were then digitally re-sized in front of green screens). Ultimately Elio & Linda felt that any of these issues were manageable if planned out well enough, and it remains a strong contender for a prequel adaptation.
 * The Regency of Aegon III - The Dance of the Dragons ended in exhaustion, and it took Westeros a full generation to recover. Much of the realm had been gutted by dragon-fire, degenerating into chaos as roving bands of former soldiers turned outlaw as long and fierce winter set in, which brought a plague with it. In many areas the fighting continued for years, particularly the private war between the ironborn and the surviving Lannisters. Most of the Targaryens and their dragons were dead, leaving only Rhaenyra's underaged son to sit the throne. The war had ended in a stalemate, so it was decided that instead of one regent, a regency council made up of seven people would rule for the boy-king, with members chosen from both sides. The regents engaged in byzantine court politics, intrigues and assassinations, as each jockeyed for power amidst the ashes.
 * Elio & Linda actually felt this is a very interesting prequel era, and Martin is writing a prequel novella about it which is almost as long for the one on the Dance itself. Also, the scale isn't quite as large and expensive as a Dance TV series. However, they dismissed that it is one of the five pitch ideas HBO ordered: much like the Sons of the Dragon, it is a direct sequel to the Dance of the Dragons, and wouldn't really work if done out of order. Even moreso than the Sons of the Dragon, characters during the Regency base their actions and allegiances on what they or their parents did during the Dance, and it would take too long to explain all of that backstory. Also, the Regency hasn't been mentioned in the original TV series. Thus, like the Sons of the Dragon, Elio & Linda feel that the most likely scenario is that if the Dance of the Dragons is greenlit as a TV series, the Regency storylines would be adapted as a direct sequel to that (i.e. either seasons 6 to 8 or so of a Dance TV series, or an outright sequel TV series to that, restarting with its own first season).
 * The "Blood of Dragons" era, Aegon III's sons & the Conquest of Dorne - a loosely-defined era when Aegon III's sons Daeron I the Young Dragon and Baelor the Blessed struggle with attempts to conquer still-independent Dorne and reform the Faith of the Seven. Through it all, Aegon III's younger brother Viserys II Targaryen is the real power behind the throne, serving as Hand of the King to both of his nephews and trying to rein in their political follies.
 * Elio & Linda greatly enjoy this time period, and have been running an online text-based RPG for years which is set during it. Still, they dismiss out of hand that it is one of the five pitches HBO could consider. While logistically relatively easy to do, there isn't one core narrative so much as several overlapping subplots. It has never been mentioned in the main TV series, and barely in the animated featurettes. Moreover, the characters and their identities would take too long to explain without prior setup from a Regency TV series. While it could be adapted in a future anthology, HBO would not possibly be considered in it as a pitch idea at this time.
 * The Reign of Aegon IV, the Unworthy - Viserys II's son takes the throne as Aegon IV, the most corrupt king in the history of Westeros. Gluttonous, petty, and lustful, having no less than nine official mistresses during his reign.
 * While Martin has always toyed with the idea of a prequel novella covering the intrigues of this era, he confirmed it is not one of the five pitch ideas HBO ordered.
 * The First Blackfyre Rebellion - Aegon IV stupidly legitimized all of his bastard children on his deathbed, including Daemon Blackfyre. Considered the best living swordsman in Westeros, he founded a rival cadet branch of House Targaryen known as House Blackfyre. Meanwhile, Aegon IV's legitimate son Daeron II united Dorne with the Iron Throne through marriage-alliance with his new bride. To win their favor and cement the alliance, Daeron II appointed multiple Dornishmen to high royal offices. The Great Houses eventually split between a pro-Dornish faction around Daeron II, and an anti-Dornish faction around Daemon Blackfyre. Civil war broke out when Daemon Blackfyre tried to seize the throne for himself, though all the Great Houses sided with Daeron II Targaryen. Ultimately Daemon Blackfyre died in the climactic battle of the war, but his numerous sons fled over the Narrow Sea, where they would launch four subsequent Blackfyre Rebellions over the next 60 years.
 * While this prequel era is fairly easy to do from a logistical standpoint, it isn't as large or expansive as the Targaryen Conquest or Dance of the Dragons. The war was fairly short, lasting one year, and had a relatively small cast of characters. Moreover, the original TV series has never mentioned the name "Blackfyre" in a live-action episode - only in the animated featurettes, and never presenting the Blackfyres as prominently as the Conquest or the Dance. On top of this, it may simply overlap with the Tales of Dunk and Egg, which will tell the story of the second through fifth and final rebellions. The graphic novel adaptation of the Tales of Dunk & Egg, for example, simply covered the First Blackfyre Rebellion through extended flashback. Just as Robert's Rebellion is the backstory to the main A Song of Ice and Fire series, the First Blackfyre Rebellion is the backstory to the Tales of Dunk & Egg: not so much a stand-alone story, but more about each gets revealed as their main series advances.
 * The Tales of Dunk and Egg - follows the adventures of Prince Aegon "Egg" Targaryen (Maester Aemon'solder brother) as he serves as a squire for the poor knight Duncan the Tall, as they wander around Westeros and get into a series of adventures. The series starts 90 years before the War of the Five Kings, when Aegon is a young boy 13th in line to the throne, but through a series of mishaps he will one day become King Aegon V, the Unlikely, and Duncan will become his Lord Commander of the Kingsguard. Westeros is struck by a terrible plague early in their adventures, throwing the realm into chaos: to the east, the Blackfyres in the Free Cities plot new rebellions to retake Westeros; to the west, the ironborn take advantage of the confusion to raid the coasts; to the north, the wildlings are emboldened to unite behind a new King-Beyond-the-Wall to attack the Starks; to the south, tensions with newly-incorporated Dorne remain high. This is also the only prequel era that Martin actually presented as a POV narrative in the style of the main novels, so the characters are very detailed (the other prequel novellas are written in the style of in-universe history books).
 * Martin directly confirmed that the Tales of Dunk & Egg is not one of the pitches to HBO nor will it be until the prequel novellas are finished.
 * Young Tywin Lannister and the Reyne Rebellion - in the background of the late reign of King Aegon V, when he is an old man, House Lannister's rule over The Westerlands is being undermined by its upstart vassals House Reyne, and the incompetence of its own weak-willed leader, Tytos Lannister. Tytos's young son Tywin, however, rises to rebuild his family's power and glory. After fighting in the Fifth Blackfyre Rebellion (also called the "War of the Ninepenny Kings"), Tywin returns home to Casterly Rock and begins to wrest power back from the Reynes, resorting in a short but bloody rebellion.
 * While Martin said that no living characters from the original TV series would appear in the prequel pitches, he may have made an exception for this (Tywin himself being the only major returning character, and obviously played by a new and much younger actor). Technically this is part of the Tales of Dunk & Egg era, but still its own distinct story going on parallel to it (Aegon V doesn't even need to directly appear, as he is only mentioned in passing from written messages).
 * Because Tywin is such an important character, Martin actually worked out the backstory of the Reyne Rebellion in unpublished notes many years before The World of Ice and Fire was published, and didn't develop it specifically for that sourcebook. Martin posted the "History of the Westerlands" chapter from the World book which contains it as a free sample on his personal website (click this link to read it). The print version in the World book was slightly edited down compared to the free online sample.
 * Similar to the Histories & Lore animated featurettes on the Targaryen Conquest and the Dance of the Dragons, the Season 7 Blu-ray set also included a longer-than-usual animated featurette on the Reyne Rebellion "The Rains of Castamere (Histories & Lore)", narrated by Jaime Lannister. The video streamlines many smaller details but gives a good summary of the Lannister-Reyne conflict. It wasn't officially a super-sized video like the 20 and 40 minute specials, but most Histories & Lore videos are only 2-3 minutes long, while this video on the Reyne Rebellion was 5 minutes long. Its presence in the Season 7 Blu-ray set might be a hint that HBO is trying to seed fan interest in it as a prequel project.
 * Robert's Rebellion - soon after the Fifth Blackfyre Rebellion, Aerys II Targaryen takes the throne. His reign starts with great promise but he gradually descends into insanity. Many hope that his son Prince Rhaegar Targaryen will succeed him before lasting damage is done - only for Rhaegar to suddenly "abduct" Lyanna Stark, the betrothed of Robert Baratheon. When her father and eldest brother come to the royal court to demand her return, Aerys has them both publicly executed - sparking off a rebellion that will topple the Targaryen dynasty after nearly three centuries.
 * Martin confirmed this is not one of the pitches submitted to HBO and he opposes ever adapting it, even as stand-alone prequel novellas.

Potential prequels set beyond Westeros
Elio & Linda assume that Martin meant at face value his comment that one of the fifth prequel pitches was not "set in Westeros", and that he didn't just mean parts of another prequel might visit other lands. For example, the Targaryen Conquest might briefly show Valyria in Essos, while the Dance of the Dragons would probably involve characters making short visits to the Free Cities to hire mercenary armies, etc. Still, if Martin truly meant one of them is a full narrative whose primary setting isn't Westeros, Elio & Linda felt that one possibility was head and shoulders above all the rest, to the point that the choice seemed obvious:


 * Nymeria and the 10,000 ships of the Rhoynar - the story of the Rhoynish Wars, and how the Rhoynar people fled to Westeros and conquered Dorne, becoming the modern Dornishmen. Around 1,000 years ago (700 years before the Targaryen Conquest of Westeros), the mighty Valyrian Freehold was locked in a massive continent-spanning war with a rival super-power, the independent city-states of the Rhoynar people. The Valyrians established their own rival city states in western Essos, which would later become the Free Cities, who encroached on Rhoynar lands and holdings in a series of wars that lasted two and a half centuries. In the final and largest war, the Rhoynar united to make one last attempt to drive off the Valyrians. The Rhoynar raised the largest land army in history, a quarter of a million men (and women), and marched against the main Valyrian colony at Volantis. The Valyrians may have had Dragons and fire-magic, but the Rhoynar had their own water-magic, with water-wizards calling down water-spouts to kill dragons, and summoning huge tidal waves that swept entire armies and towns away. This climaxed at the Battle of Volantis, when the Valyrians counter-attacked with an army of three hundred dragons and shattered the Rhoynar host (the biggest battle in human history). Princess Nymeria then led the surviving Rhoynar to flee on every ship they could find, an Aeneid-like quest for a new home as they wandered around the Summer Sea, visiting Sothoryos (filled with giant monsters, actual dinosaurs, and King Kong sized gorillas), then Naath and the utopian Summer Islands, before finally arriving in Dorne. Nor did the story end there, as the Rhoynar allied with the local House Martell to conquer and unify the rest of Dorne for the first time.
 * While Martin never wrote a "prequel novella" as such for this event, it does have an extensive sub-chapter in the World book. It has a clear, linear outline, a compelling narrative, and instead of multiple sprawling subplots running in parallel, it would be fairly tightly focused on Nymeria as the main character. Fans have also been excited by the events in it: massive armies clashing, armies of dragons, Valyria at the height of its power (a few characters named "Targaryen" might plausibly appear, but aren't mentioned in the text), and seeing the exotic lands and creatures of the Summer Sea.
 * On the other hand, as Elio & Linda point out, the special effects budget required would be astronomical. To the point that HBO might consider making it as a miniseries or even a big-budget theatrical movie, rather than a long-form TV series.
 * One of the five potential showrunners is, suspiciously, Max Borenstein - famous as the screenwriter on the successful reboot movie series of Godzilla and King-King: Skull Island. He very much seems to be the kind of writer that HBO would hire to do a story featuring massive CGI creatures while still keeping the narrative grounded with the human characters, the way Borenstein's Godzilla series did (in contrast, "Young Tywin" doesn't really seem to match the style and skillset Borenstein is noted for).

In contrast to the numerous possible prequels set in Westeros, Elio & Linda felt that HBO would have little interest in other stories besides Nymeria & the Rhoynar versus Valyria. Most have been so-little mentioned in the original TV series that they wouldn't have name recognition or crossover appeal to casual viewers of it, while others would have budget or scale issues. Moreover, while interesting outlines exist for several, found in The World of Ice & Fire sourcebook, Martin never wrote a "prequel novella" for any of these the way he did several prequel eras in Westeros (he didn't even write a prequel novella for Nymeria, just a long chapter in the World book). Other potential ideas are interesting, possibly for video game spinoffs, but probably aren't among the first wave of five pitches HBO ordered:


 * The Doom of Valyria - when Valyria's capital city and mighty empire were destroyed in a single day, when a cataclysmic volcanic eruption destroyed them and all their dragons - except for the Targaryens, who had fled to Westeros.
 * This couldn't possibly sustain a full TV series, any more than the explosion of Mt. Vesuvius and destruction of Pompeii could. If they wanted to show "pre-Doom Valyria", at the height of its power, they'd show the Rhoynish Wars and Nymeria.
 * The Century of Blood - the chaotic century after the Doom when the Valyrians' now-leaderless colonies across Essos declared their independence and started competing for land and resources in a chaotic free-for-all, ultimately forming the modern Free Cities as they were later known. Volantis, oldest and largest, tried to conquer the other eight and nearly succeeded, but was gradually pushed back when the others (such as Braavos and Pentos) allied with each other to repel them. Meanwhile, with no dragons left to protect the frontiers, the Dothraki launched into their great era of expansion, exploding across the entire continent of Essos in a wave of conquest.
 * Elio & Linda felt that there was storyline worth exploring here, and it does have name recognition: the TV series did visit Braavos, Pentos, and Volantis, and it would see the return of the Dothraki. The biggest issue is simply that there is no prequel novella for it, only broad outlines Martin gave (though more than he did for the Long Night in Westeros). HBO would have to invent many of the specifics and characters. It would be similar in tone to Game of Thrones, featuring political backstabbing and shifting political alliances (the Free Cities are inspired by the medieval Italian city-states, and the Doom of Valyria with the fall of Rome). The time scale is also an issue, unless HBO wants to focus on the last generation of it when the wars drew to a close. Ultimately, while Elio & Linda felt this was a plausible prequel era to explore, it would not be a first pick for HBO.
 * The Summer Islands - Sothoryos, the third known continent, is located south of Essos; the Summer Islands, an archipelago off the coast of Sothoryos, are essentially their world's equivalent of Marvel's Wakanda - beautiful and utopian Africa-themed city-states, ruled by merchant princes (and princesses) who command vast fleets of trading ships, selling spices and other goods in ports as distant as Oldtown, Braavos, and Qarth. Thousands of years ago, when the Summer Islanders first began exploring the oceans around their homes, they were targeted by slaver-raids from Essos. One woman, Princess Xanda Qo, conquered and unified the Summer Islands in order to fend off this external threat.
 * There is no prequel novella for this, only the Summer Islands chapter in the World book. It could still make a linear, fairly easy to make and compelling narrative, exploring a new corner of their world beyond Westeros (the Summer Islands are actually in closer contact with Westeros, both geographically and through trade, than the Dothraki are). However, the Summer Islands have been barely mentioned in the original TV series, and all the Summer Islander characters who did appear in the main novels were cut for time. This is to the point that hardly anything about their culture and society has appeared in the original TV series, so it wouldn't have much name recognition for casual viewers.
 * The Golden Empire of Yi Ti - Yi Ti is their world's fantasy analogue of Imperial China. It is located far to the east of Qarth (about as far east of Qarth as Slaver's Bay is distant from Qarth to the west). The World of Ice and Fire gives an extensive chapter on its flourishing civilization - the oldest and most advanced in the world, having continuously existed since the Long Night itself, eight thousand years ago. Yi Ti has a hundred rival princedoms each as powerful as one of the Seven Kingdoms, whose internal intrigues and civil wars make Westeros's pale in comparison. Yi Ti is also beset by hostile powers on its borders, such as the constant attacks of the Jogos Nhai mounted raiders from the north, mountain tribes to the west, and to the east, the sorcerers and shadow-binders of Asshai and the Shadow Lands, and further still, Carcosa - a strange city ruled by its yellow king.
 * Similar to the Summer Islands, it simply has no connection to the original TV series. Even the name "Yi Ti" has never been said in a live-action TV episode, only briefly in a few of the animated featurettes (the "Summer Islands" have at least been mentioned in passing in a few TV episodes).

Conclusion

 * Elio & Linda did not anticipate that HBO would order a pilot pitch based on the Long Night and the Age of Heroes, as there is so little established information about these events. Nonetheless, to the surprise of many, this was the first prequel for which a pilot was officially ordered. In hindsight, it does have very good name recognition with even casual viewers of the TV series (everyone knows the White Walkers as the major antagonists of the original TV series).
 * It still appears highly probable that two of the prequel pitches will be "The Targaryen Conquest" and "The Dance of the Dragons". They are the most extensive prequel eras to the main novels themselves, in terms of the amount of prequel novella material that Martin already wrote for them. Most importantly, HBO seemed to be seeding the ground for interest in them by making special super-sized animated featurettes on each (20 minutes on the Dance of the Dragons in Season 5, then 40 minutes on the Targaryen Conquest in Season 7).
 * As Elio & Linda pointed out, due to plot structure, "The Sons of the Dragon" and "The Regency of Aegon III" - two other large and distinctly defined prequel eras with their own novellas - probably were not among the original five pitches, because they are really direct sequels to prior stories. The story content of "The Sons of the Dragon" would probably be the later seasons of a 5-6 year "Conquest & Rebellion" TV series, and the Regency would only be made as a follow-up to a live-action Dance of the Dragons series.

Further developments

 * In July 2018, a an extensive report leaked to Game of Thrones Wiki itself that Max Borenstein's prequel is about the Doom of Valyria, titled Empire of Ash. This is the prequel Martin was alluding to as "not set in Westeros".  HBO has yet to confirm the accuracy of the leak.  The leak went on to say that Borenstein's prequel was actually the first pitched, back in 2016, and that Borenstein and Goldman's projects were always the two front-runners:  they are the only two that have full writing staffs for immediate development, while the other three ideas were pitches that HBO was still considering on a long development scale (i.e. planning out successor shows for the next decade or more, as a major ongoing franchise).
 * Martin confirmed that one of the five announced pitch ideas was officially rejected. Its identity is still unknown, but was very probably whatever Bryan Cogman was working on - given that in October 2018 it was announced that he had signed an exclusive development deal with Amazon, leaving HBO.
 * The identity of the sixth prequel pitch is still unknown: one of the original two that Martin said were pitched (the other one of those two was apparently Borenstein's).
 * Martin went on to remark in October 2018 that he had suggested two additional prequel ideas to HBO, besides the five that were announced - but it is unclear if they were ever formal pitches or just ideas he discussed with them. For that matter, it's also unclear if he was including the previously rejected sixth prequel pitch among these "two other ideas".  Thus there are at least seven potential stories which Martin himself thinks could sustain prequel TV projects, though HBO has passed on three of them.
 * Leading up to the release of Martin's Fire & Blood: Volume 1 on November 20th, 2018, Martin admitted that "at least two" of the remaining four prequel pitches were directly based on material in it. Fire & Blood is an outgrowth of The World of Ice & Fire sourcebook, an in-universe history book about the first half of the Targaryen dynasty's reign, starting with Aegon I and ending with Aegon III.  This all but confirms the already strong evidence that two of the prequels being considered are the Targaryen Conquest and the Dance of the Dragons.
 * Thus it appears that the four prequel pitches still being considered by HBO are the Long Night (Jane Goldman), the Doom of Valyria (Max Borenstein), Targaryen Conquest (possibly Brian Helgeland), and the Dance of the Dragons (possibly Carly Wray).