Kelly ClarksonDeparting judge Simon Cowell was supposed to be the center of attention in the 'American Idol' season 9 finale. But ironically, it was the former 'American Idol' winners who stole the show during his special farewell tribute segment, which also featured the return of former judge Paula Abdul.

In a true show-stopping moment, winners Kelly Clarkson, Ruben Studdard, Fantasia Barrino, Carrie Underwood, Taylor Hicks, Jordin Sparks and Kris Allen took to the stage to sing 'Together We Are One' by Delta Goodrem, during which they were joined by a revolving door of 'Idol' finalists that included everyone from Kimberly Caldwell to Constantine Maroulis and, yes, Justin Guarini.

Noticeably absent, though, was season 7 winner David Cook -- the only 'Idol' winner who did not take part in the group performance. According to Twitter, Cook was attending a charity event for cancer in Kansas City. An official word from Cook's camp has yet to be released.

Check out the clip after the jump.