Justin Bieber loves making surprise cameos at music festivals!
In March, the pop star crashed Skrillex's set at Ultra Musica Festival to perform as an energetic robot!
On Sunday, the singer surprised audiences when he came out on stage during Jack U's set at the Hard Summer Music Festival in Pomona, California!
[ Related: Justin Bieber Is Making New Music With WHO?! ]
The 21-year-old rocked a grungy Metallica T-shirt as he hit the stage with Diplo and Skrillex –when the four artists performed their hit collaboration Where Are U Now!
Check out the footage (below) to see the crowd go wild for Bieberoni & co.'s performance:
[Image via WENN.]
Tags: diplo, footage, hard summer music festival, jack u, justin bieber, metallica, music minute, perform, skrillex