Trystane Martell

"You are my queen. The Queen of Dorne."

- Trystane Martell to his betrothed, Myrcella Baratheon.

Trystane Martell is a recurring character in the fifth season, debuting in "The House of Black and White", portrayed by Toby Sebastian. Trystane is the son and only child of Prince Doran Martell.

Background
Prince Trystane is a member of House Martell, the ruling house of Dorne. He is the son of Prince Doran Martell, Lord of Sunspear and Prince of Dorne.

Season 2
Trystane is proposed as a potential marriage candidate for Princess Myrcella Baratheon by her uncle, Hand of the King Tyrion Lannister. The alliance with the Prince of Dorne is accepted and Myrcella is sent to Dorne as a ward of House Martell.

Season 5
Trystane is briefly seen walking and flirting with his betrothed Myrcella Baratheon in the Water Gardens during the argument between Ellaria Sand and Prince Doran Martell.

When Jaime Lannister and Bronn enter the Water Gardens, Trystane is again taking a walk with Myrcella, with Trystane suggesting they should ask Doran to have them married the next day. Myrcella asks if he only wants to marry her because they are both from Great Houses, but Trystane cuts her off with a passionate kiss. Doran, observing the happy couple, muses to Areo Hotah that they don't realize how much danger they are in and that they must be protected.

While kissing Myrcella, Trystane encounters Bronn and Jaime in the Gardens. Although he introduces himself courteously enough, he is clearly suspicious, having heard no news of Jaime's visit to Dorne; his suspicions are aroused further when he sees bloodstains on the stolen robes Jaime and Bronn are wearing. Although Bronn cautions him not to do something stupid, Trystane reaches for his sword, forcing Bronn to knock him out, to Myrcella's distress. Jaime then attempts to take Myrcella out of the palace, but he and Bronn are then attacked by Trystane's cousins, the Sand Snakes. The skirmish ends when all five of the intruders are arrested by Areo Hotah and his guards.

Doran invites Trystane, Myrcella, Ellaria and Jaime to drinking and eat with him. There, he promises Jaime that he does not want a war with the Lannisters and that he will send Myrcella back to King's Landing. However, Trystane and Myrcella's betrothal is to stand, which means Trystane will accompany his betrothed to the capital. He will also take up Oberyn's vacant seat on the Small Council, to further cement the alliance between Dorne and the Iron Throne. Jaime accepts these terms.

Jaime then brings up the matter of Bronn, who is still imprisoned as a result of his aggression on the prince. Doran defers to Trystane to decide, as he must learn how to punish lawbreakers if he must one day rule. Trystane agrees to let Bronn go on one condition: he will receive the same thing that he inflicted upon him. This meets with his father's approval and Bronn is brought before them and Aero elbows him hard across the face.

In the books
In the A Song of Ice and Fire novels, Prince Trystane is the youngest son of Prince Doran Martell, the ruler of Dorne, and third in the Martell line of succession. He has olive skin and straight black hair. He is two years older than Myrcella Baratheon, making him about 12 years old when they are betrothed.

The casting announcement for Trystane in Season 5 describes him as the "heir to Dorne", even though in the books he has an older brother named Quentyn, and his father's eldest child and heir is actually his daughter Arianne. This may mean that Quentyn has been cut from the TV series.

It still isn't clear if Arianne exists in the TV continuity or not. She is a major character and even a POV narrator in the books. On the other hand, in the books Arianne is furious that her father is treating his son Quentyn as his heir, despite the fact that under Dornish law she should inherit ahead of him. Later she discovers that this is because her father wanted to keep options for a vital marriage-alliance open, but he never thought of this as brushing Arianne aside. In any case, the supplemental bluray material has never that Dorne follows equal primogeniture, unlike the rest of the continent. In stray mentions throughout Season 4, when the TV series could have introduced that women have an equal chance of inheriting lordships in Dorne, they avoided it. A "Lord Blackmont" appeared in the Season 4 premiere, when in the books House Blackmont is ruled by a woman. When Oberyn recounts to Tyrion how he traveled to Casterly Rock when Tyrion was a baby, he says that his father took him on the trip - while in the books, it was his mother, the Ruling Princess of Dorne. Indeed, Dorne's equal primogeniture laws are one of its most prominent cultural features, setting it apart from the rest of the continent - as well as directly tying into Myrcella Baratheon's major subplot in Dorne, as Arianne hopes to press the token excuse that under Dornish law, Myrcella would inherit the Iron Throne ahead of her brother Tommen.

A major point standing against an omission of Arianne is that the only dialogue which previously mentioned Trystane (Season 2's "What is Dead May Never Die") described him as Doran's "youngest son" - indirectly establishing that TV-Trystane isn't an only child, and at the least, that Doran has another son who is older than him, so TV-Trystane cannot be the "heir to Dorne". So either the character description is misworded, or the TV series will have to establish an internal retcon with facts stated in Season 2.

Elio Garcia of Westeros.org suspects that the casting description of Trystane is simply mistaken, pointing out that he was earlier described as Doran's "youngest" son, and also that the casting description said that Tywin had arranged Trystane's betrothal to Myrcella, when it was actually Tyrion who arranged the betrothal (though Tywin subsequently supported Tyrion's action when he heard about it). Elio went so far as to reach out to his contacts at HBO to determine if this was simply a mistake by someone in the HBO PR department, and he did get a response, but it consisted entirely of a terse "no comment". Elio stated his belief that while he is somewhat nervous that there has been no mention of Arianne yet (or the Greyjoy uncles and other Northmen bannermen who appear at this point in the books), the SDCC casting announcement was in no way meant to be comprehensive, and as of yet he sees no specific reason to believe that Arianne has been outright omitted from the TV continuity.