Rita Ora has been cast as Mia, Christian Grey’s adopted sister, in the film version of EL James's best-selling erotic novel, Fifty Shades of Grey.(Reuters)
Rita Ora has been cast as Mia, Christian Grey’s adopted sister, in the film version of EL James\'s best-selling erotic novel, Fifty Shades of Grey.(Reuters)

Rita Ora has been cast as Mia, Christian Grey's adopted sister, in the film version of EL James' best-selling erotic novel, Fifty Shades of Grey.

The 23-year-old took to her Twitter account to confirm the news.

"It's official! I've been cast in @FiftyShades of Grey as Christian's sister Mia. #FiftyShades," Ora tweeted.

Ora had previously in 2004 appeared in British film Spivs as Rosanna, and made a cameo appearance in Fast & Furious 6.

Meanwhile, Irish actor/model Jamie Dornan plays Grey, and American actress Dakota Johnson will be seen as Anastasia Steele. Sam Taylor-Johnson is directing from a screenplay by Kelly Marcel.

"I'm a fairly worldly guy. I grew up in a very liberal place. I'm not saying we had a playroom, but I'm not shocked by [the sex in the book]. It's essential to tell the story. I can't believe films that don't invoke the sexual side of it. So it works for me," Dornan said of his character to Entertainment Weekly.

The 24-year-old daughter of actors Melanie Griffith and Don Johnson, had described the erotic book as "an incredible love story."

"I just really understand it," Johnson told the publication, "I think it's an incredible love story and that's why it's affected so many people. Erica (EL James) did a really good job of explaining how that just can happen sometimes and you have this chemical pull to someone. Adding in the sex makes it perfect. Sometimes you feel a little bit naughty and that's okay."

The film will also star Eloise Mumford, Luke Grimes, Victor Rasuk, Jennifer Ehle, and Max Martini. The film will hit theaters on 13 February, 2015.