At 42, the mother of three (twins Hazel and Phinnaeus, 5, and Henry, 2) is celebrating her fourth turn as the cover girl for PEOPLE's Most Beautiful. While the star of the upcoming film Eat, Pray, Love is as lovely as ever, old pal George Clooney says he knows her secret. "It has nothing to do with the way she looks," he says. "It has everything to do with who she is."
VIDEO: Julia's Changing Looks