Emma Stone thinks Colin Firth is ''coming out of his shell''.

The 25-year-old actress believes their new movie 'Magic in the Moonlight' will show another side of her co-star that no one has seen before.

Speaking on 'The David Letterman Show', she joked: ''I think he tricked us all in believing that he's this charming, lovely fellow. But he's really - you'll see - I think he's coming out of his shell. He's a nightmare.''

Colin - who is defined by his role as Mr Darcy in 'Pride and Prejudice' - will star alongside Emma as Stanley in the romantic comedy set in 1920s France.

The movie follows the story of an Englishman, who is employed and sent to the French Riviera to help uncover a possible swindle, but professional and personal complications ensure it doesn't go to plan.

Meanwhile, director Woody Allen has already cast Emma in his upcoming untitled film, which is filming in Rhode Island, after being so impressed by her performance as Sophie in 'Magic in the Moonlight'.

'Magic in the Moonlight' will hit UK cinemas on July 25.