Sienna Miller Talks Bradley Cooper's Unrecognizable Appearance in 'American Sniper'

Sienna Miller shows off her vintage style while attending the opening night of Inside Rolls-Royce at the Saatchi Gallery on Thursday (November 13) in London, England.

The 32-year-old actress recently gushed about her co-star Bradley Cooper in their upcoming film American Sniper.

PHOTOS: Check out the latest pics of Sienna Miller

“His performance is completely compelling. He’s just unrecognizable,” Sienna shared to Entertainment Weekly. “He was training four to six hours a day. He put on 40 pounds of muscle. He looked and sounded like a different person. I’m pretty sure he didn’t break character for the entire thing. He dived into this completely head-first. It was an amazing thing to be around.”

FYI: Sienna is wearing a Reformation jumpsuit.

15+ pictures inside of Sienna Miller at Inside Rolls-Royce…