Justin Bieber and Taylor Swift 'Baby' in Los Angeles

Teen idol joins country star on stage in Los Angeles for 'Baby'

"You think you've heard LOUD screaming in your life. Then @justinbieber comes out and does a surprise song during your show. Woah. Unreal," Taylor Swift tweeted last night after concluding a show at the Staples Center in Los Angeles in which the teen heartthrob turned up to perform his massive hit "Baby." As you can see in this fan-shot footage from the gig, pretty much everyone in the house was flipping out for Bieber, including Swift herself, who seems overjoyed by his presence.