HBO's Game of Thrones prequel continues to add to its roster.

Ahead of its early summer production start, Miranda Richardson (The Crying Game) has joined the cast of the pilot created by Jane Goldman and George R.R. Martin.

The drama, picked up to pilot last June, is set thousands of years before the events of the HBO flagship. The story chronicles the world's descent from the golden Age of Heroes into its darkest hour. A logline from the network teased the plot without divulging any specifics: "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."

Details on Richardson's character are, in typical Game of Thrones fashion, being kept under wraps. She joins a cast that also includes Naomi Watts, who is playing a charismatic socialite hiding a dark secret. The rest of the previously announced cast includes Josh Whitehouse (Poldark), Naomi Ackie (Star Wars: Episode IX), Denise Gough (Guerrilla), Jamie Campbell Bower (Twilight), Sheila Atim (Harlots), Ivanno Jeremiah (Black Mirror), Georgie Henley (The Chronicles of Narnia), Alex Sharp (To the Bone) and Toby Regbo (The Fantastic Beasts: The Crimes of Grindewald).

The pilot is based on a story from Goldman and Martin, with the teleplay credited to Goldman. Goldman will also serve as showrunner. In addition to Goldman and Martin, executive producers on the series include current Game of Thrones producer Vince Gerardis, as well as Damages and Bloodline co-creator Daniel Zelman and Jim Danger Gray. Chris Symes will serve as a co-EP. SJ Clarkson will direct the pilot. Sara Lee Hess will also be an EP.

Goldman and Martin's Game of Thrones prequel is the first of several potential series set in the world of Westeros to move forward at HBO beyond the script phase. In May 2017, a multitude of writers were revealed by the pay cabler to be working on what Martin himself has described as "successor shows." Those writers include Goldman, Max Borenstein (Kong: Skull Island), Brian Helgeland (Legend), Carly Wray (Westworld) and Game of Thrones veteran Bryan Cogman. Game of Thrones creators and showrunners David Benioff and Dan Weiss are not involved in the successor show effort, focusing instead on the forthcoming final season of Game of Thrones after more than a decade spent wandering the world of the Seven Kingdoms.

Richardson's credits also include two Harry Potter features, Stronger, Girlfriends, Empire of the Sun, Damage, Enchanted April, Fatherland, Tom & Viv, The Lost Prince and Curfew. She is repped by Paradigm and the U.K.'s Independent.