PEOPLE.com) -- Kelly Osbourne, 25, hit the Emmy Awards red carpet on Sunday looking slimmer than ever in a black, form-fitting Tony Ward gown.
What's the secret to her new sleek physique?
"Ever since Dancing with the Stars, I've tried to get in at least a half hour of cardio a day -- nothing too crazy," she tells PEOPLE. "My trainer Sarah Hagaman is amazing! She knows how to motivate me to go that extra bit without frustrating me."
The actress -- who hits up Hagaman's Blue Clay Fitness gym four times a week -- now has a little extra incentive when it comes to keeping her looks camera-ready: She's joined Joan Rivers as a panelist for the "Fashion Police" on E!