Bloodmoon

HBO has officially ordered a pilot episode for a Game of Thrones prequel series about the Long Night during the Age of Heroes, set some 8,000 years before the War of the Five Kings in the original TV series. Jane Goldman will be showrunners, with George R.R. Martin attached as a co-producer.

Overview
While a pilot has been ordered into production, there is no guarantee that HBO will order production of a full TV series based on it. Moreover, Martin clarified that three other prequel projects are still in active development - Goldman's was just the first to be officially ordered (though this may indicate HBO's confidence in it). As Martin understands it, HBO's intention is to have at least one and possibly all three of the other prequel pitches film pilot episodes, then pick one of these to develop based on the strength of the pilots. He also believes that HBO intends to hopefully premiere the first prequel series in 2020, about one year after the original TV series has its finale - enough time later that they don't overlap, but close enough that interest in the franchise as a whole doesn't start to fade.

As of June 2018, Martin stated that only the pilot script order has been finished: no directors, filming locations, or actors were in place yet.

Title
The final title of this prequel project has not been determined yet. Martin stated that he would personally chose "The Long Night" but he doesn't have final say, and that he thinks HBO would probably want to put "Game of Thrones" in it so audiences will know they're part of the same franchise. Thus this article uses "Game of Thrones: The Long Night" as a placeholder for navigation purposes, pending further updates.