Justin Bieber is all about surprises this summer. Back in July, the 17-year-old pop superstar took fans by surprise when he joined Selena Gomez onstage in Costa Mesa, California, and on Tuesday night, he made another unexpected appearance when he joined Taylor Swift onstage for a duet of his hit "Baby" at her Speak Now tour stop in Los Angeles.

Video footage of the duo's performance at the Staples Center hit the Internet shortly after the concert. It shows the music superstars sharing song verses and Bieber spitting a brief rap midway through the number.

Swift took to Twitter hours later to applaud her roaring concert audience and their overwhelming reaction to the Bieb's surprise appearance. "Dear amazing LA crowd tonight, God only knows what I'd be without you," she wrote. "You think you've heard LOUD screaming in your life. Then @justinbieber comes out and does a surprise song during your show. Woah. Unreal."

Bieber responded to the country-pop darling, tweeting, "@taylorswift13 we should do that more often. :) great show! #muchlove."

It was nothing but love as Bieber's manager, Scooter Braun, also chimed in on the surprise concert cameo. "Had to keep it a secret all day. But @justinbieber just came out and sang BABY with @taylorswift13 at STAPLES. EPIC ROAR! #greatmoment," he wrote on Twitter.

Bieber also recently collaborated with Chris Brown. Earlier this month, the Video Music Award nominee showed off his rap skills on "Ladies Love Me," a track that appears on Breezy's Boy in Detention mixtape.