Justin Bieber Surprises Selena Gomez and Fans Onstage at Her Concert (VIDEO)

Selena Gomez fans got their money's worth at the Sunday night show at the Pacific Amphitheatre in Costa Mesa, Calif.

In the middle of the concert, Selena Gomez, in a sparkly pink dress, was surprised by her beau Justin Bieber, who took to the stage.

The 17-year-old heartthrob greeted his lady with a hug before singing “Favorite Girl.”

Bieber also sang the classic breakup ode: Justin Timberlake's "Cry Me a River."

"Had a #greatnight and surprised the people. felt good to be on stage. nothing is changing that. #REAL," Bieber tweeted after the show.

He also tweeted: "@selenagomez u did great tonight. proud of u."

"I've been working so hard, I'm taking a month off," Bieber recently told The Hollywood Reporter. He also expressed enthusiasm about the new album he's working on, MTV Music reported. "More excited than ever to get back in the studio and make this #newalbum," Bieber tweeted. "Miss the tour and want to give u all new music. #BELIEVE I do this because i love music. #REAL."

Gomez turned 19 on Friday and celebrated her birthday with Bieber.

Below is the video where Justin Bieber Surprise at Selena Gomez Concert 7/24/11 O.C. Fair: