Justin Bieber Surprises Fans At Taylor Swift Concert (VIDEO)

Fans got an extra special surprise Tuesday night at Taylor Swift's concert at LA's Staples Center -- the one and only Justin Bieber!
The audience reacted with squeals of delight when Swift brought her mega-star friend on stage to perform a duet of his hit song, "Baby," with her.

Watch the video and see for yourself.

Later that night, Taylor tweeted: "You think you've heard LOUD screaming in your lifr. Then @justinbieber comes out and does a surprise song during your show. Whoa. Unreal."