The Firework hitmaker was performing at the Rock in Rio Festival in Rio de Janeiro on Sunday (27Sep15) when she invited an audience member, thought to be called Rayane, onto the stage.

The fan wrapped her arms around the singer's neck and began smooching her, and Katy told the audience, "She's kissing my neck!"

Katy made a variety of shocked faces as Rayane clutched her tightly, rested her head on the star's breasts and repeatedly kissed her hand.

The Roar star eventually eased away from her admirer, and as Rayane was about to leave the stage, Katy slapped her bottom.

Rayane then ran back to her idol and pinched the star's butt in return, before a man arrived on the steps of the stage to guide her away.