Actress Sienna Miller was “nervous” about acting alongside super-slender Keira Knightley — as she had been forced to put on weight for the role, reports.

Miller appears with Knightley in forthcoming movie The Edge Of Love, and the normally svelte star was asked to pile on the pounds for picture, which tells the story of poet Dylan Thomas.

Miller, 26, admits having to gain weight for the film worried her, as she feared her trim co-star would emphasize her added bulk.

“I was actually pretty nervous about acting alongside Keira because my part required me to put on weight,” Miller says. “I stuffed my face for the months we were in production. I had huge fry-up breakfasts, pasties for lunch and lots of toasties (toasted sandwiches). Then, I had to face seeing myself alongside Keira, who is the most beautiful woman in the world.”