Snooki, Kristin Cavallari, and 18 More Reality TV Stars Who Made It Big (PHOTOS)

It's hard to believe a hitmaker like Kelly got her start on a then-fledgling singing contest called American Idol 10 years ago. But talent is talent, and this powerful singer has proven her longevity in the biz. With more than 23 million albums sold worldwide, Kelly is considered the most successful Idol contestant to date. She recently returned to the realm of televised singing competitions as a musical mentor on Duets.