Keira Knightley Giggled While Filming Love Scene

Keira Knightley struggled to compose herself while filming a love scene for her new movie The Duchess.

The British beauty -- who reportedly earned $32 Million in 2007 -- says she couldn't stop laughing when she saw her co-star Dominic Cooper's outfit for the 18th-Century romp.

She reveals, "Sex scenes are never the easiest scenes to film and you are meant to be very supportive of each other. But when Dominic came out in a skin-coloured nappy I just completely lost it.

"I just couldn't stop laughing. The director did actually come over and said: 'Come on, pull yourself together, this is a serious work here' but I could not help it - there was this man standing there in a skin-colored nappy!"

Knightley, 23, has previously insisted she has no problem stripping off in front of the camera.

The actress -- who happily took off her bra for a sex scene with Cillian Murphy in the June 2008 film The Edge of Love -- said, "It was very simple. It was a sex scene and I never like them when they've got bras on. So when asked I said, 'alright then'."

The Duchess, which also stars Ralph Fiennes, is due for release on September 12.