"Fifty Shades of Grey" movie cast just got bigger: Rita Ora has been cast as Christian Grey's adopted sister Mia. She'll join Jamie Dornan and Dakota Johnson as Christian Grey and Anastasia Steele in the movie adaptation of "Fifty Shades of Grey."

Rita Ora is best known as a singer signed to Jay-Z's Roc Nation label, Entertainment Weekly reports. The British pop star has just a few movie titles under her belt, so her joining the "Fifty Shades of Grey" cast will be a high-profile introduction to her acting.

Rita Ora announced her role in the film on her Twitter. She tweeted to her fans: "It's official! I've been cast in @FiftyShades of Grey as Christian's sister Mia. #FiftyShades"

Rita Ora will join a cast of fresh faces, including Max Martini Christian Grey's bodyguard, Jamie Dornan (Christian Grey), Dakota Johnson (Anastasia Steele), Eloise Mumford (Anatasia's best friend Kate) and Luke Grimes (Christian's brother Elliot). Victor Rasuk will portray Anastasia's close friend José and Jennifer Ehle will be Anastasia's mother, Carla. Sam Taylor-Johnson is directing the movie adaptation of E.L. James' erotic novel trilogy, which has sold more than 90 million copies, E! News reports.

"Fifty Shades of Grey" just began shooting Monday and is schedule to hit theaters in February 2015, just in time for Valentine's Day.

Check out photos of the cast above!