Milly Alcock, House of the Dragon Breakout Star, Cast as DC Universe Supergirl

It was reportedly down to Alcock, Zombies star Meg Donnelly, and CODA star Emilia Jones, per Deadline, with Alcock finally landing the coveted role of Kara Zor-El, cousin to the Man of Steel.

The actress quickly became a fan-favorite on HBO's Game of Thrones prequel series as Rhaenyra Targaryen. Only a massive mid-season time jump cost her that gig as there was no way she could pass for the aged-up Rhaenyra. Emma D'Arcy took over the role and will continue in it.

It's a high profile get for Alcock, but also one for Gunn as Alcock is still riding a buzz of critical and fan praise for her performance in the genre series, with many fans lamenting that she had to leave.

"Milly is a fantastically talented young actor, and I'm incredibly excited about her being a part of the DCU," Gunn posted to his Instagram on Monday. The director admitted that, like many, he first became aware of her from House of the Dragon, but he was "blown away by her varied auditions and screen tests for Supergirl."

"She embodies Kara as envisioned by Tom King, Bliquis Evely, and Ana Nogueira," Gunn added. Supergirl: Woman of Tomorrow is based on the comic book mini-series of the same name by King and Evely, while Nogueira has been working on the screenplay.

As for Alcock, she's looking at an even higher profile for her career with the multi-film deal. Like Marvel Cinematic Universe stars, Alcock is expected to make appearances in films other than her own. In fact, according to the Deadline report, she's expected to show up in other films before jumping into her solo film.

What's unknown, though, is if one of those films will feature Kara's cousin Kal-El. David Corenswet was revealed last year as the actor picked to bring DC Comics' most iconic superhero to life in Superman: Legacy, which is written and directed by Gunn himself.

With Alcock locked in, work on the solo film could be set to begin as early as this fall. Superman: Legacy is set to begin filming in March so it could be said that Alcock's casting comes just in time, should there be a role for her in that film.

Other than helping to spin her out into her solo film, another reason it might make sense for Alcock to at least have a small appearance in Legacy is that Gunn and Safran have already said she's going to serve as a contrast to Superman's hopeful optimism.

"We will see the difference between Superman, who was sent to Earth and raised by loving parents from the time he was an infant," Gunn said earlier this month, "versus Supergirl, raised on a rock, a chip off of Krypton, and who watched everyone around her die and be killed in terrible ways for the first 14 years of her life and then come to Earth."

That certainly suggests a darker, more morose personality -- which is also in line with King and Evely's comic book series. That project saw Supergirl take to the stars to deal with always being in her cousin's shadow. He is, after all, the biggest and most beloved superhero on the planet.

Alcock follows in the heels of other live-action Supergirls like Helen Slater from the 1984 film, Smallville's Laura Vandervoort, The Flash's Sasha Calle, and of course, The CW's own Supergirl, Melissa Benoist.