Jennifer Lopez surprised fans when she unexpectedly joined rapper Iggy Azalea during her set at the We Can Survive charity concert on Friday (24Oct14).

The Jenny From The Block hitmaker took to the stage wearing a silver bra and skirt and duetted with Azalea on their raunchy collaboration Booty, completing the performance by repeatedly tapping each other on the rear.

Ariana Grande also appeared at the Hollywood Bowl in Los Angeles for a five-song set but had to apologise to the audience for technical difficulties, blaming the issue on her outfit.

She wrote on Twitter.com ahead of the show, "Two show day!!! now if only my costume hadn't ripped after the last performance & if only the other options weren't stuck on the plane... hopefully we'll have the wardrobe situation sorted out by then lol (laugh out loud)."

Other acts included Taylor Swift, Pharrell Williams, Gwen Stefani, Paramore, Lady Antebellum and Sia, who performed her set with her back to the audience.

The annual We Can Survive concert raises money for breast cancer research.