Dakota Johnson may have bared all in Fifty Shades of Grey but revealed she used a bum double for the hardcore S&M punishment scene.

The 25-year-old actress stripped down for her debut lead role but admitted she didn’t want to experience the pain of getting hit with the belt as described in the book. Speaking to the Daily Star the daughter of Don Johnson and Melanie Griffiths said: “There was a close up of a bum getting hit with a belt.

“That was not my bum, because I didn’t want to get hit with a belt.”

Dakota, who has had small roles in The Social Network and 21 Jump Street, wowed on the red carpet this week at the UK premiere for Fifty Shades. The leading lady took the plunge in the dress which was almost cut to her navel. Showing she’s a bit of all-white, the star flaunted her enviably trim frame in the flowing frock with thin straps and glittering detail. Her hair was worn in a sleek, straight style and she made her ensemble pop with a splash of purple lipstick.

Dark-haired stunner Dakota, who plays Anastasia Steele in the S&M-mad movie, completed her look with a silver clutch bag and a large statement ring.