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OTRC: Selena Gomez concert 'crashed' by Justin Bieber (Video)

Justin Bieber makes a surprise appearance at his girlfriend Selena Gomez's concert at the O.C. Fair in Costa Mesa, California on July 24, 2011, as seen in this fan-made video. (youtube.com/user/amandacapellino)

Fresh off his wedding crashing experience, Justin Bieber made a surprise appearance at a different event over the weekend.

The teen pop singer walked on stage at his girlfriend Selena Gomez's concert at the Pacific Amphitheatre at the OC Fair in Costa Mesa, California on Sunday, July 24, to the delight of scores of screaming fans.

She introduced Bieber, 17, and the two hugged. He then gave a solo performance of Justin Timberlake's Grammy-winning 2002 hit "Cry Me A River" (see video below).

"Had a #greatnight and surprised the people," Bieber Tweeted that night. "Felt good to be on stage. nothing is changing that. @selenagomez u did great tonight. proud of u."

Gomez, who celebrated her 19th birthday on July 22, has not commented about the concert publicly.

Bieber and Gomez were first linked together in late 2010. The two have tended to keep details of their relationship private when asked about it in interviews.

The couple drew the wrath of some of Bieber's fans when they stepped out together at the 2011 Academy Awards in February. Many posted nasty comments and even death threats against Gomez on Twitter.

"I can't shut out all of it," Gomez said on the ABC show "Good Morning America" in June, when asked about how she handles the negative remarks. "I'm human so I read it. I know what's being said, obviously, but I have better things in my life and I do try to ignore it and I have incredible supporters."

In mid-July, Bieber and Gomez made headlines by crashing a wedding of a Los Angeles couple, who later spoke about it to the press.

"We were shocked as anyone to kind of see Justin Bieber scamper by," the groom, Rob McCool, said on "Good Morning America." "I was actually wiping cake off my face. To see him come running by - it was a very surreal experience."

Bieber is one of the most popular young pop singers in the world and is currently working on a new album. His 2010 record, "My World 2.0," has sold more than 2 million copies in the United States.

Check out a fan-made video of Justin Bieber performing along during Selena Gomez's concert at the Orange County Fair below.

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