The "Game of Thrones" prequel has found its first cast member: Naomi Watts.
The Oscar-nominated actress will star in the untitled pilot created by Jane Goldman ("Kingsman," "Kickass," "X-Men: First Class") and author George R.R. Martin.
The prequel is set thousands of years before the events of "Game of Thrones," which will conclude with an eighth and final season next year on HBO. It chronicles the world's descent from the golden Age of Heroes into its darkest hour.
As the network described it, "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."
Watts will play “a charismatic socialite hiding a dark secret.”
HBO began developing a handful of "Game of Thrones" spinoffs last year, but only Goldman's script (based on a story by herself and Martin) received a greenlight to make a pilot.
The pilot will likely be filmed in early 2019, once more actors have been cast and a director has been selected. HBO has said that any successor series would not air until the final season of "Game of Thrones" was over.