Dakota Johnson and Charlie Hunnam will take on the roles of Anastasia Steele and Christian Grey, respectively, in the anticipated big-screen adaptation of the sexy novel.

The news was tweeted by novel author E.L. James on Monday morning: ‘Good moaning all. Hold on to your hats…’ she wrote shortly before making the announcements.

Dakota, 23, previously appeared in The Social Network – in which she shared a love scene with Justin Timberlake – and had small roles in 21 Jump Street, The Five-Year Engagement and Beastly.

She is the daughter of Don Johnson, best known for TV shows Miami Vice and Nash Bridges, and his actress ex-wife Melanie Griffith.

It’s thought producers cast Dakota because they wanted a young, up-and-coming actress to play the role of virginal Anastasia, who embarks on an intense voyage of sexual discovery with her S&M-loving boss Christian.

Charlie, who is 33 years old and British, stars in the dark biker thriller Sons Of Anarchy as Jackson ‘Jax’ Teller and also appeared in Guillermo del Toro’s robot epic Pacific Rim.

The castings close waves of rumours about who would take on the roles – Emma Watson, Imogen Poots, Armie Hammer and Ian Somerhalder, among many others, were at one time tied to a main role on the film.

Fifty Shades Of Grey will be directed by Sam Taylor-Johnson (Nowhere Boy), based off the adapted script by Kelly Marcel (Terra Nova).

The film is currently slated for release in August 2014.