Marquis Rodriquez. Picture: Instagram

The "Game of Thrones" prequel pilot is beefing up its cast.

Marquis Rodriquez, John Simm, Richard McCabe, John Heffernan, and Dixie Egerickx have all been cast in series regular roles, reports variety.com.

As with all things "Game of Thrones," the exact nature of the characters each will be playing is being kept under tight wraps.

Rodriguez will next be seen starring in the Netflix miniseries "When They See Us" from director Ava DuVernay, which is based on the true story of the Central Park Five. He also had a role in the Marvel-Netflix shows "Luke Cage" and "Iron Fist".

Simm's previous television credits include "Collateral", "Doctor Who", "The Catch" "Life on Mars" and "The Canterbury Tales".

McCabe has appeared in shows such as "Philip K. Dick's Electric Dreams," "Harlots," "Collateral," and "Peaky Blinders." 

Heffernan's TV credits include "Dracula," "Brexit," "Collateral," "The Crown," and "Luther".

Egerickx recently wrapped on "The Secret Garden" and previously appeared in the films "Summerland" and "The Little Stranger". 

The five join previously announced cast members Naomi Watts, Josh Whitehouse, Naomi Ackie, Denise Gough, Jamie Campbell Bower, Sheila Atim, Ivanno Jeremiah, Georgie Henley, Alex Sharp, Toby Regbo and Miranda Richardson.

Taking place thousands of years before the events of "Game of Thrones," the new show 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.

Jane Goldman co-created the project with George R.R. Martin, whose "A Song of Ice and Fire" novel series serves as the basis for "Game of Thrones".

Goldman and Martin have written the story, with Goldman writing the teleplay. She will also serve as showrunner. The news comes as "Game of Thrones" prepares to launch its highly-anticipated eighth and final season on April 14.