Rita Ora has been cast in 'Fifty Shades of Grey'.

The 23-year-old singer will play the adopted sister of S&M-loving billionaire Christian Grey in the film adaptation of E.L. James' best selling novel.

She tweeted: ''It's official! I've been cast in Fifty Shades Of Grey as Christian's sister Mia (sic)''

Rita will star alongside Jamie Dornan, who plays Christian, and Dakota Johnson who is his lover, Anastasia Steele, in the movie which is being directed by Sam Taylor-Johnson.

The blonde beauty - who studied acting when she attended the Sylvia Young Theatre School in London as a teenager - was previously seen in 2004 film 'Spivs' when she was 14, and had a cameo role in 'Fast and Furious 6', where she impressed co-star Vin Diesel.

Meanwhile, James is ''terrified'' about the film adaptation of her book and the author admits she feels huge pressure for the movie to be a success and she is determined to get things ''right''.

She previously said: ''I'm terrified. Completely. I've been terrified from the moment I published the book. My mother was terrified of everything, and so am I. It's a terrible way to grow up. You don't expect this kind of success.''