The Game of Thrones prequel series doesn't have an official title. However, A Song of Ice and Fire creator, George R.R. Martin has an idea of what it should be called: The Long Night.
HBO made their first big post-Game of Thrones move by ordering the pilot for a new prequel series set to arrive after the first show concludes. This is just one of several spinoff ideas in development for Game of Thrones, and may never make it to air since a pilot order is not the same as a series order. Yet based on Martin's unofficial title, the potential series has a lot of excitement and mayhem to adapt. It also happens to involve everyone's favorite ice zombies, the White Walkers.
Martin addressed the pilot of the prequel on his own website. In addition, to clarifying that he's not involved in the series, other than in a consultant capacity, Martin did shed some details on the prequel. Martin wrote:
This one really puts the PRE in prequel, since it is set not ninety years before GAME OF THRONES (like Dunk & Egg), or a few hundred years, but rather ten thousand years (well, assuming the oral histories of the First Men are accurate, but there are maesters at the Citadel who insist it has only been half that long). We’re very early in the process, of course, with the pilot order just in, so we don’t have a director yet, or a cast, or a location, or even a title. (My vote would be THE LONG NIGHT, which says it all, but I’d be surprised if that’s where we end up. More likely HBO will want to work the phrase “game of thrones” in there somewhere.)
The Long Night has been mentioned previously on Game of Thrones. Yet it's only been really in passing and only the most hardcore of fans, probably the ones who have read the books, will recognize the term. However, the Long Night is an incredibly important period in the history of Game of Thrones. The Long Night occurred more than eight thousand years before the first season of Game of Thrones. As the name suggests, it refers to a time when the entire country of Westeros was gripped by a literal darkness and the Long Night occurred in the middle of one of the longest winters ever. (Any Game of Thrones fan knows that winter can last much more longer than a single season in the universe.) The Long Night is also when the White Walkers, reportedly, made their first appearance.
Martin is probably correct that the eventual title of the series won't be The Long Night. Game of Thrones will probably be worked into the title somewhere. Not only for the name recognition but to suggest how important the prequel series will be to understanding the lore of Game of Thrones and where the story (likely) ends. After all, going into the series' final season, the Night King and his White Walkers are the biggest antagonists, but there's so very little known about them. The prequel series could (and should) change all of that, if Martin's tease is correct.
Going directly from the end of Game of Thrones, where Winter has finally come, to a series about the Long Night would be the most natural transition too. With so few episodes in Game of Thrones season 8 (only six) there's not going to be enough time to answer every question fans have about the White Walkers and their creation. The prequel series could provide those answers and put the engdame of Game of Thrones to an even wider context. The only downside is that the prequel series could be much more high fantasy than people are used to seeing. Part of the appeal of Game of Thrones are the very human stories and characters in an unbelievable setting. Undoubtedly the prequel will have some element of that, but it also could be much more of a straight zombie series.
Game of Thrones will return for season 8 sometime in 2019.
Source: George R.R. Martin