Charlie Hunnam and Dakota Johnson cast in Fifty Shades of Grey

Charlie Hunnam and Dakota Johnson have scored the hotly contested lead roles in the upcoming film adaptation of the saucy novel Fifty Shades of Grey.

After many months of speculation, Universal confirmed the casting of Johnson (The Social Network, Ben & Kate) as Anastasia Steele, the college student who becomes enraptured by 27-year-old, S&M loving billionaire Christian Grey.

Hunnam (Pacific Rim, Sons of Anarchy) will take on the role of Grey.

Sam Taylor-Johnson will direct the picture, based on a screenplay by Kelly Marcel.

The original text – first born as Twilight fan fiction – was penned by E.L. James.

The book has become a publishing phenomenon, selling more than 70 million copies worldwide.

Fifty Shades of Grey hits cinemas July 31, 2014.