Justin Bieber Surprises Selena Gomez Onstage (VIDEO)
But that's not all he sang!
Justin Biebs also sang a hit from Mr. J.T., Justin Timberlake! Check out SelGo's guy covering "Cry Me a River."
Following the show, Justin wrote of his gal's performance, tweeting:
“@selenagomez u did great tonight. proud of u.”
Selena turned 19 on Friday and probably spent the weekend with her beau celebrating. What do you think of this hot teen couple? Will they last? Sound off in the comments, and be sure to follow Celebuzz on Twitter, Facebook and Tumblr to get the latest breaking celebrity news!