Justin Bieber Surprises Fans With "Baby" Duet at Taylor Swift's Concert!

This is the best version of Justin Bieber's "Baby" yet! The 17-year-old heartthrob surprised fans in L.A. last night by singing a duet with Taylor Swift during her concert.

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Justin kept his word! Taylor previously covered his hit song "Baby" during a show in Toronto and Justin Tweeted her, "heard you sang BABY at your concert in TO. thank u for the love ... might have to come by and stop in on a show."

And he did!

"You think you've heard LOUD screaming in your life. Then @justinbieber comes out and does a surprise song during your show," Taylor Tweeted about her good friend Selena Gomez's boyfriend. "Woah. Unreal."

We're screaming just watching the video clip! And it sounds like Justin may want to do it again.

"@taylorswift13 we should do that more often," Justin Tweeted. "great show! #muchlove."

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Watch the clip, below!