The cast of the Game of Thrones has expanded once again with the addition of five new cast members.

Among the five are ever-popular British actor John Simm, known for his roles as The Master in Doctor Who and DCI Sam Tyler in Life on Mars.

Fellow Brit Richard McCabe, who won a Tony for his Broadway role opposite Dame Helen Mirren in The Audience, has also joined the cast.

The other newbies are Marquis Rodriguez (When They See Us), John Heffernan (The Crown, Brexit: The Uncivil War), and 13-year-old Dixie Egerickx (Patrick Melrose).

According to The Hollywood Reporter, they've all landed series regular roles, bringing the total number of series regulars to 16 (!).

Harry Potter actress Miranda Richardson joined the cast of the prequel last week. Two-time Oscar nominee Naomi Watts has been attached for several months and she's understood to be playing a "a charismatic socialite hiding a dark secret."

Other confirmed cast members include Denise Gough (Colette), Josh Whitehouse (Poldark), Toby Regbo (Fantastic Beasts: The Crimes of Grindelwald), Ivanno Jeremiah (Humans), Georgie Henley (the Chronicles of Narnia films), Naomi Ackie (Star Wars: Episode IX), Jamie Campbell Bower (the Twilight movies), Sheila Atim (Harlots), and Alex Sharp (Broadway’s The Curious Incident of the Dog in the Night-Time).

Game of Thrones creator and author George R.R. Martin and Jane Goldman (Kingsman: The Secret Service) have collaborated on the story for the new series, which takes place thousands of years before what we saw go down in Westeros. Goldman will write the script and Martin will serve as an executive producer, and the prequel pilot is expected to air in 2020.

In the meantime, the eighth and final season of regular Game of Thrones is set to premiere April 21 on HBO, and it's unlikely to be a low-key farewell.

Are you excited for the Game of Thrones prequel?