Keira Knightley has confessed she couldn’t keep a straight face while filming sex scenes for The Duchess. The 24-year-old actress revealed she kept getting the giggles as her co-star Dominic Cooper, 30, had to wear a nappy, The Sun reports. Keira said: “During the sex scene I was luckily fully clothed, but he had to wear this skin-coloured nappy.” She continued: “Sex scenes are never the easiest and you’re meant to be very supportive of each other, but I just completely lost it. “The director had to tell me, ‘Pull yourself together’.” Dominic said of his ‘nappy’: “We just laughed at it continually. It was a relaxed atmosphere. We had complete trust and faith in the director that it would be very tasteful. “We had to just laugh our way through it all because at times it was ridiculous.” He continued: “They are certainly very intimate scenes. I sometimes can’t stand them because in films sometimes they are just thrown in for no apparent reason. “Certainly with a relationship of these two characters it was essential that we saw how close and intimate they are, having a desperate need for belonging and love.