Keira KnightleyKeira Knightley has revealed she found it hard to keep a straight face while filming sex scenes for new movie The Duchess.

Co-star Dominic Cooper had to wear flesh-coloured concealing underwear for the scene to make him appear naked on camera - but the effect was comic, not sexy, close up.

Keira explained recently: “I couldn’t stop laughing. He’s a very good-looking guy but he’s standing there naked apart from a skin-coloured nappy.

“It’s the most unsexy thing ever. The director even had to ask if I could be a little more supportive and I had to say ‘no - he’s wearing a nappy!’”