
The casting of the movie, to be directed by British filmmaker and artist Sam Taylor-Johnson of "Nowhere Boy" fame, has been one of the most hotly anticipated secrets in Hollywood.
But instead of big names, the producers have gone for up-and-coming stars.
Hunnam starred in this summer's sci-fi blockbuster "Pacific Rim" while US actress and model Johnson is the daughter of veteran "Miami Vice" star Don Johnson and Oscar-nominated actress Melanie Griffith.
"I am delighted to let you know that the lovely Dakota Johnson has agreed to be our Anastasia in the film adaptation of Fifty Shades of Grey," author James said on Twitter.