With one epic fantasy series winding down, HBO is gearing up for another.

The premium cable network is coming on board to co-produce and air the BBC's massive adaptation of Philip Pullman's "His Dark Materials. This comes on the heels of news that the BBC has already ordered a second season of the fantasy epic.

The adaptation is believed to be one of the most expensive and expansive British dramas ever. It's based on Pullman’s bestselling books "Northern Lights" ("The Golden Compass" in the U.S.), "The Subtle Knife" and "The Amber Spyglass." The series stars Dafne Keen, James McAvoy, Ruth Wilson and Lin-Manuel Miranda.

"His Dark Materials" follows Lyra (Dafne Keen), a seemingly ordinary but brave young woman from another world. Lyra’s search for a kidnapped friend uncovers a sinister plot involving stolen children, and becomes a quest to understand a mysterious phenomenon called Dust. As she journeys through the worlds, including our own, Lyra meets a determined and courageous boy called Will. Together they encounter extraordinary beings and dangerous secrets, with the fate of both the living — and the dead — in their hands.

The project is currently filming in the U.K. and is not likely to broadcast until late 2019 or sometime in 2020.

HBO will lose one of its centerpiece shows, "Game of Thrones," when it concludes next spring. It is developing a prequel spinoff, but "His Dark Materials" could also help fill the very big programming hole left behind.