Caitlin Tadlock

Justin Bieber surprised fans at an Los Angeles Taylor Swift concert on Tuesday night, August 23rd. The teen sensation ran on T Swift's stage after she finished "You Belong To Me", slapping hands of the fans that were going into a frenzy at the mere sight of him.

Bieber and Swift did a duet of Bieber's hit, "Baby" complete with his back up dancers. As soon as the duet ended Bieber ran off stage and Swift finished the concert by herself, singing songs off her album, Speak Now.

Tuesday night's concert at the Staples Center in LA was the first of four sold out concerts Taylor Swift is putting on. For the video of Justin Bieber and Swift's "Baby" click the "Videos" tab.