Katy Perry: "E.T." on "American Idol" with Kanye West

Teaming up on the grandest of stages, Katy Perry joined forces with Kanye West on Thursday night's (April 21) episode of "American Idol".

The "Firework" songstress and her hip-hop partner's pre-taped duet kicked off with Kanye appearing via music video - with the "All Of the Lights" rapper surprisingly joining Katy onstage moments later.