4 more stars have been added to the 'House of the Dragon' cast. See who they're playing here.

• Actors Eve Best, Steve Toussaint, Sonoya Mizuno, and Rhys Ifans will costar in "House of the Dragon."
• You might recognize Sonoya Mizuno from "Ex Machina" and "Devs," or the rom-com hit "Crazy Rich Asians."

The first "Game of Thrones" prequel series, "House of the Dragon," just boosted its star power with four new cast members.

On Thursday, HBO announced Eve Best, Steve Toussaint, Sonoya Mizuno, and Rhys Ifans as new costars in the show.

"House of the Dragon" takes place about 200 years prior to "Game of Thrones," with a focus on a bloody Targaryen civil war that involved various members of the royal court and other notable Houses.

Here's who the new cast members are playing, according to HBO:

• Steve Toussaint as Lord Corlys Velaryon aka "The Sea Snake." "The lord of House Velaryon, a Valyrian bloodline as old as House Targaryen, 'The Sea Snake,' is the most famed nautical adventurer in the history of Westeros. He built his house into a powerful seat that is even richer than the Lannisters and that claims the largest navy in the world."
• Eve Best as Princess Rhaenys Velaryon. "A dragonrider and wife to Lord Corlys Velaryon, 'The Queen Who Never Was' was passed over as heir to the throne at the Great Council because the realm favored her cousin, Viserys, simply for being male."
• Rhys Ifans as Otto Hightower. "The Hand of the King, who loyally and faithfully serves both his king and his realm. As the Hand sees it, the greatest threat to the realm is the king's brother, Daemon, and his position as heir to the throne."
• Sonoya Mizuno as Mysaria. "She came to Westeros with nothing, sold more times than she can recall, and could have wilted...but instead she rose to become the most trusted - and most unlikely - ally of Prince Daemon Targaryen, the heir to the throne."

Sci-fi fans will be familiar with Sonoya Mizuno, who costarred in the 2014 film "Ex Machina," Netflix's 2018 series "Maniac," and most recently played the lead in FX's 2020 series "Devs." She also played the bride, Araminta, in 2018's rom-com hit "Crazy Rich Asians."

Mizuno and the other actors join a list of notable names already announced by HBO.

Paddy Considine ("The Outsider," "Hot Fuzz") will star as King Viserys, the fifth Targaryen ruler in Westeros.

Matt Smith ("The Crown," "Doctor Who") will play Prince Daemon Targaryen, while Emma D'Arcy ("Wanderlust") will star as Princess Rhaenyra Targaryen. Olivia Cooke ("Ready Player One") also joins the cast as Alicent Hightower, the daughter of the Hand of the King during King Viserys I rule in Westeros.

You can read everything else we know so far about "House of the Dragon" in our report here. For a look at all the other spinoff and prequel ideas that could be in the works at HBO, read our deep dive here.