HBO has unleashed a flood of casting news about a planned prequel to its hugely successful Game of Thrones series, which will air its final season later this year. Details are scarce, but the company confirmed the prequel will be set thousands of years before the events of the original series, fueling even more fan speculation about which aspects of George R.R. Martin's vast fictional universe will be featured.

We do get some strong hints from the official HBO website. The prequel "chronicles the world's descent from the Golden Age of Heroes into its darkest hour," HBO announced. "From the horrifying secrets of Westeros' history to the true origin of the White Walkers, the mysteries of the East to the Starks of legend, only one thing is for sure: It's not the story we think we know."

A Long Night?

The Age of Heroes in the Martinverse timeline coincides with two key mythical figures, Bran the Builder—a House Stark forebear famous for building the great Wall of Westeros (the one that came crashing down in the final moments of last season)—and Lann the Clever, a forefather of House Lannister. This is also right around the time of the infamous "Long Night" occasionally referenced on Game of Thrones, a winter that lasted a very long time, when mankind first waged war against the White Walkers, ultimately joining forces with the Children of the Forest to defeat them. Martin himself referred to the prequel as The Long Night, and while HBO has not confirmed it, it'll do for a working title.

We can be fairly certain that the prequel won't be about Robert's Rebellion, which takes place within 20 years or so of the events of the original HBO series. Martin himself wrote on his blog in 2017 that, by the time he finishes A Song of Ice and Fire, readers will know all there is to know about that part of Westeros history (although, given his famously glacial writing pace, that could be several years off). "There would be no surprises or revelations left in such a show, just the acting out of conflicts whose resolutions you already know," he wrote. "It would feel too much like a twice-told tale."

Nor will it be an adaption of his popular Dunk & Egg spinoff novellas, since he's not done writing those either. "I don't want to repeat what happened with Game of Thrones itself, where the show gets ahead of the books," he wrote.

At one point there were five prequel projects in development for HBO. One fell by the wayside, and the others are presumably on the back burner for now. HBO officially ordered The Long Night pilot last June, created by Martin and Jane Goldman as co-executive producers, with the latter penning the teleplay. It will be directed by SJ Clarkson (Jessica Jones, The Defenders). Production should begin later this year on the approved prequel pilot, with shooting locations likely to include Northern Ireland (where most of the Winterfell footage has been shot in the past) and the Canary Islands.

As for the cast, Naomi Watts (Twin Peaks, The Return) signed up early on to play "a charismatic socialite hiding a dark secret," along with Josh Whitehouse (Poldark) in an unspecified role (perhaps Bran the Builder?). The rest of the cast showcases an impressive diversity that frankly was often missing from the original series, including Denise Gough and Jamie Campbell Bower, both of whom made a splash playing queer or gender-bending characters (Gough as the cross-dressing Mathilde de Morny in the biopic Colette, and Campbell Bower as young Grindelwald, Dumbledore's love interest in the Harry Potter franchise).

Also just announced as cast members: Naomi Ackie (Star Wars: Episode IX), Sheila Atim (Harlots), Ivanno Jeremiah (Black Mirror, Humans), Georgie Henley (The Chronicles of Narnia), Alex Sharp (To the Bone), and Toby Regbo (Fantastic Beasts: The Crimes of Grindelwald).

While there's no guarantee for a full series order, HBO has said if it does move forward with the project, the prequel definitely won't air until at least a year after Game of Thrones ends. So we're looking at 2020 or beyond before our next TV foray into the mythical world of Westeros.