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.
And the crowd went wild.
Their song choice doesn't come as a surprise, however. According to Billboard, Swift covered Bieber's "Baby" during her shows in Montreal and Toronto in July.
Swift is currently on her "Speak Now" tour, which wraps up at Madison Square Garden in November. For more details on Swift's show, head over to Billboard.