Rita Ora says '50 Shades of Grey' film will be the ''most amazing shock ever''.

The 23-year-old singer stars as Christian Grey's adopted sister Mia in ''incredible'' Sam Taylor-Wood's forthcoming film alongside Jamie Dornan and Dakota Johnson - who have been cast as the sado-masochistic millionaire and his lover Anastasia Steele respectively.

This role will be Rita's most important part to date, she has previously appeared in Universal's 'Fast & Furious 6' as a London street racer. Prior to that she starred in the 2004 film 'Spivs' playing Rosanna.

Rita told MTV News: ''I was nervous because it was the first time I ever did a movie with words but it was so nice. The director Sam, she was incredible, so it was all love.''

The blonde beauty added ''I'm so excited'' about the film claiming it's ''gonna be the biggest and most amazing shock ever''.

Rita will be making a ''sexy'' transformation for her role and is hoping to surprise audiences.

She told E! News: ''It's a surprise. Hopefully you won't recognise me.'' And added: ''It's sexy!''

The film adaptation of E.L. James' erotic novel - which won't be as sexually explicit as the book - will be released on February 14, 2015.