SJ Clarkson (the upcoming 'Star Trek' feature) will direct the pilot, which will be toplined by Naomi Ackie (J.J. Abrams' upcoming 'Star Wars').

The cast of HBO's Game of Thrones prequel is coming together.

The premium cable network has cast eight rising stars to join Naomi Watts and Josh Whitehouse in the pilot from writers Jane Goldman and franchise mastermind George R.R. Martin. Additionally, SJ Clarkson (Jessica Jones, Succession and the upcoming Star Trek feature) has been tapped to direct the pilot.

Cast as series regulars are Naomi Ackie (next appearing in J.J. Abrams' Star Wars), Denise Gough (Guerrilla, Tony-nominated for Angels in America), Jamie Campbell Bower (Sweeney Todd, Twilight, Mortal Instruments), 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).

As with all things Game of Thrones, details about their characters are being kept under wraps. The only character detail that has been revealed is that Watts is taking on the role of a charismatic socialite hiding a dark secret.

The drama 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."

The Game of Thrones successor show was created by Goldman and A Song of Ice and Fire author Martin. The pilot, which was picked up by HBO in June, is based on a story from Goldman and Martin, with the teleplay credited to Goldman. She also will serve as showrunner. In addition to Goldman and Martin, executive producers on the project include Clarkson, James Farrell, Jim Danger Gray, current Game of Thrones producer Vince Gerardis, Damages and Bloodline co-creator Daniel Zelman and Chris Symes, with the latter on board as a co-exec producer.

Clarkson will become the first female director of a Star Trek feature when she takes the helm of Star Trek 4, from Abrams. Her credits include BBC/Netflix's Collateral and pilots for Marvel's The Defenders and Jessica Jones, as well as episodes of Orange Is the New Black, Bates Motel, Dexter and HBO/Cinemax's Banshee. She is repped by WME and Curtis Brown in the U.K.

Ackie, who is repped by CAA, the U.K.'s Hamilton Hodell, Cinetic Media and Peikoff Mahan, will next appear in Abrams' Star Wars: Episode IX, which is due out in December. She most recently appeared in Idris Elba's feature directorial debut Yardie and has a key role on Channel 4/Hulu's The Bisexual.

Gough's credits include an Olivier Award and Critics Circle Theater Award for her performance in the play People Places and Things. She starred in the feature Colette alongside Keira Knightley and next appears in The Kid Who Would Be King; Juliet, Naked; and The Torture Report. Gough is repped by UTA and Independent Talent Group in the U.K.

Bower, repped by Paradigm, the U.K.'s Dalzell and Beresford, Vector and Sloane Offer, counts the Twilight franchise, TNT's short-lived Will, Starz's Camelot and AMC's The Prisoner among her credits.

Atim won an Olivier Award for her role in Girl From the North Country, and she also appeared opposite Mark Rylance and Andre Holland in Othello. Atim is with Middleweek Newtown Talent Management, Fourward and Jackoway Austen Tyerman.

Brit Jeremiah, repped by Scott Marshall Partners and Luber Roklin, counts episodes of Doctor Who and Humans among his credits. He next appears in the U.K. feature The Flood, opposite Game of Thrones favorites Lena Headey and Iain Glen.

Henley, with ICM, Hamilton Hodell, art2perform and Peikoff Mahan, is no stranger to blockbuster franchises, having started her career playing Lucy in all three Chronicles of Narnia features.

Sharp, a May graduate from Juilliard, won a 2015 Tony Award for best lead actor in a play for his Broadway debut in The Curious Incident of the Dog in the Night-Time. He recently wrapped The Hustle and appeared in How to Talk to Girls at Parties. Sharp is repped by CAA and Elin Flack Management.

Regbo appeared in Netflix's The Last Kingdom and recently reprised his role as Young Dumbledore in November's Fantastic Beasts: The Crimes of Grindelwald. He is currently shooting Netflix's Medici, opposite Game of Thrones grad Richard Madden. Regbo's credits include The CW's Reign. He is repped by Authentic Talent and Literary Management, Independent Talent Group and attorney Karl Austen.

Additional casting on the Game of Thrones prequel is expected to be announced at a later date.