While fans understandably have lots of questions—like which families and houses will be involved—we do know some key details already, many of which have been gleaned from inadvertent spoilers from Martin himself. (Oops!) Here is everything we know so far.
1. It will likely be titled The Long Night.
Although HBO has yet to confirm it, Martin did let it slip on his blog that the series will be titled The Long Night. Though we can't consider that a definite until the studio has announced it, it's pretty much the accepted title at this point, and even IMDb has officially adopted the moniker.
Martin did attempt to backtrack his spoiler by saying it’s not actually the title just yet. "HBO has informed me that the Jane Goldman pilot is not (yet) titled THE LONG NIGHT," he wrote on his blog. "That is certainly the title I prefer, but for the moment the pilot is still officially UNTITLED. So … mea culpa, mea culpa, mea culpa."
2. It's set about 5000 years before the events of Game of Thrones.
The prequel series is set thousands of years before the events of Game of Thrones, in the Age of Heroes. If Martin’s reveal of the title is true, it will be a bleak period, as the Long Night is what the people of Westeros call the time when darkness fell upon the Known World, and it lasted for a generation.
Martin recently made the time frame a bit clearer in an interview with Entertainment Weekly, explaining that it’s closer to 5000 years before the events in Game of Thrones, not the 10,000 years many fans had originally thought.
3. You won't hear any mention of King's Landing, the Iron Throne, or the Targaryens.
The story is set before the rise of Valyria, the city in which the House Targaryen originated. "Westeros is a very different place," Martin told Entertainment Weekly of the prequel series. "There’s no King’s Landing. There’s no Iron Throne. There are no Targaryens—Valyria has hardly begun to rise yet with its dragons and the great empire that it built. We’re dealing with a different and older world and hopefully that will be part of the fun of the series." (Though just because we won't hear about them when the series kicks off, doesn't mean they couldn't pop up later.)
4. Two-time Oscar nominee Naomi Watts will star.
So far, two of the main characters have been cast in the series. The first is two-time Oscar nominee Naomi Watts, who, according to Variety, is playing "a charismatic socialite hiding a dark secret." Fans have been speculating that because of her blonde hair and light complexion, her character could be someone related to the Lannister line.
5. George RR Martin is co-creating it with Kick-Ass, Kingsman, and X-Men screenwriter Jane Goldman.
Since it was announced the series was getting a pilot order, co-creators George RR Martin and Jane Goldman, who wrote the screenplays for Kick-Ass, X-Men: First Class, Kingsman: The Secret Service, and more, have been attached.
6. Filming is set to begin in early 2019.
Although there is no release date set for the prequel series, we do know that filming will begin in February 2019 in Belfast, Ireland—which likely means a 2020 release date (but that's just speculation). It will, of course, air on HBO.