It's war of the bums between Kylie and Pippa!

Pop princess Kylie Minogue has challenged Pippa Middleton to a royal battle of the bums. The Aussie singer has vowed to have a "bum-off" with the Duchess of Cambridge's sister at Monday's Diamond Jubilee concert.

Does it rear-ly matter? Kylie Minogue has challenged Pippa Middleton to a bum off at the Queen's Diamond Jubilee Concert where she would be performing a medley of songs. File pics/Getty Images

Pippa (28) threatened to upstage Kate on her wedding day last April, when her shapely rear stole headlines around the world. But Kylie, whose pert behind sent pulses racing in a tiny pair of gold hotpants in the video for Spinning Around, is not prepared to give up her crown just yet.

Kylie, who celebrated her 44th birthday on Monday, revealed her cheeky plan on Alan Carr's Chatty Man TV show. Asked whether she would have a "bum-off" with her rear nemesis, Kylie said: "I'm going to have to. "I'll definitely have to be like ‘Oh!', drop something and pick it up off the ground!"

Kylie is set to perform at the concert, which will celebrate the Queen's 60 years on the throne, but admitted that she is nervous about singing in front of the Royal Family. She added: "I can't tell you much about the performance, but what I can say is that I'm doing a medley. I've had a rehearsal and I had a very terrified expression! It's really exciting, nerves aside, I can't wait."u00a0 u00a0 u00a0 u00a0 u00a0u00a0