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HBO has officially greenlit a follow-up pilot to its acclaimed international hit Game of Thrones and it sounds just as massively ambitious as the original series.

The network has ordered a prequel drama from writer Jane Goldman (Kingsman: The Secret Service, X-Men: First Class, Kick-Ass) and author George R.R. Martin. The network has released an official description of the show’s storyline, and it’s another tale spread across multiple locations and clans: Taking place thousands of years before the events of Game of Thrones, the series chronicles the world’s descent from the golden Age of Heroes into its darkest hour. And only one thing is for sure: 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… it’s not the story we think we know.”

According to Martin’s books, the Age of Heroes began 10,000 years before the events in GoT. Some of the major names which could be characters in the new show include Bran the Builder (who founded House Stark and oversaw construction of The Wall and Winterfell) and Lann the Clever (who founded House Lannister). The era led into the Long Night — a winter that lasted a generation — and the greatest war against the white walkers. Then again, that’s what we think we know, and the logline for the new show says this is “not the story we think we know.”

The pilot doesn’t yet have a title. If greenlit to series, HBO has previously stated that no successor series will air until a year after GoT has its series finale. Since the eighth and final season of GoT is coming next year, the soonest we can see a successor series is 2020. If ordered to series, this will mark the first time in HBO’s history that the premium cable network has made a successor series to one of its shows.

Obviously, given the show’s timeline, it’s not expected to use any of the show’s current cast members (though the Night King making an appearance doesn’t seem out of the question). GoT showrunners David Benioff and Dan Weiss have elected not to be involved; after finishing the final season the duo will transition to penning a new series of Star Wars films for Disney.

Goldman is credited as co-creator on the drama along with Martin and will serve as showrunner. Goldman won a highly unusual bake-off that HBO put into motion last fall between five different writers, each tasked with developing a Game of Thrones follow-up series. GoT is considered a lightning-in-a-bottle hit, and the idea was to maximize the network’s chances of finding a successor that fans would embrace. Sources say the other four prequel ideas are still under consideration.

Having a new series set in Westeros from the perspective of a female showrunner should generate buzz as GoT has often provoked debate about the show’s treatment of its female characters in a fantasy world, albeit one inspired by the historical brutality of medieval Europe.

The stakes are high for HBO. The importance of the franchise to the premium cable network — and to its corporate parent Time Warner, which frequently cites the fantasy drama in investor conference calls — is tough to overstate. GoT is HBO’s most popular series of all time, averaging 23 million viewers last season in the U.S. alone. It’s also the most Emmy Award-winning drama ever made, with 38 Emmys and counting. And despite its steep price tag (the show now costs more than $15 million per episode before marketing), GoT is hugely financially lucrative; HBO owns the show, which it sells worldwide along with an array of merchandising and home video releases.

But the network should be in good hands with Goldman, a British writer with an impressive resume of popular big-screen genre titles. She began her career in journalism and writing books, then landed her own paranormal TV series, Jane Goldman Investigates, in 2003. She then partnered with director Matthew Vaughan on hits Kick-Ass, X-Men: First Class, X-Men: Days of Future Past, and the Kingsman films. She also wrote the scripts for the film adaptations of The Women in Black and Miss Peregrine’s Home for Peculiar Children. In December, it was announced that Goldman would write the script for Disney’s upcoming live-action The Little Mermaid film.

NEXT: 5 reasons we’re excited about the Game of Thrones spinoff Age of Heroes