Juno Temple has revealed she got a fright when she saw Johnny Depp transformed into mobster Whitey Bulger for the film Black Mass.

The Horns star, who plays Deborah Hussey in the film, admitted the make-up and effects team did such a good job on the Hollywood heartthrob that she was taken aback.

"They gave him an amazing transformation. He looks frightening - but in the right kind of way, the intimidating way," she said.

"It was so great to work with him like that because he is such a lovely guy, but the transformation, when he became Whitey, was like, 'Woah'. I think it will be incredible."

Johnny plays the Irish gangster in the big-screen adaptation of Dick Lehr and Gerard O'Neill's book, Black Mass: The True Story Of An Unholy Alliance Between The FBI And The Irish Mob. Benedict Cumberbatch, Joel Edgerton, Sienna Miller and Kevin Bacon also have roles in Scott Cooper's crime drama.

Juno previously told Heroine magazine that his eyes were the scariest thing about him, saying: "He had these crazy contact lenses in his eyes that almost reminded me of lizards so when you were acting with him you were genuinely quite frightened, but he was lovely, so encouraging."

Despite being afraid of her co-star, the 25-year-old actress said it was a "magical" experience working on Black Mass.

"It was incredible. It was a new experience for me because I've never done a Boston accent before, and so that was a complete challenge but so much fun, wrapping your mouth round a whole new dialect," she continued.

"Scott Cooper is one of my favourite directors of all time, and then getting to work with Johnny Depp, it was a dream job."

Horns opens in cinemas on October 29.