During an interview with an Australian radio show on Monday (28Sep15), Sarah Harris, 22, claimed the pop star was a little handsy at the annual Midsummer Night's Dream party at the Playboy Mansion in Los Angeles.

She alleges Bieber thanked her for sticking up for him when he refused to take a photo with a fellow model, but his gratitude went a little too far.

She told Australia's The Edge 96.1, "He grabbed my boob! And it was my instant reaction to just backhand him across the face.

"He kind of freaked out and didn't even say anything. And then (his date) Kylie Jenner pulled the finger at me and then security took them both out."

Harris insists the pop superstar has since apologised.

Bieber has yet to respond to Harris' claims.