Australian pop star Kylie Minogue was left red-faced when she met Pippa Middleton this summer (12) after she jokingly challenged her to a 'battle of the butts'.

The singer, who has regularly topped 'best bottom' lists since donning a pair of gold hot pants in her Spinning Around video, challenged Catherine, Duchess of Cambridge's sister to a contest to see who has the best rear after the brunette caused a sensation at the royal wedding last year (11).

Appearing on U.K. Tv this summer (12), Minogue announced she wanted a showdown with Middleton at Queen Elizabeth Ii's Diamond Jubilee, insisting, "I'm going to have to (challenge her)."

Minogue never expected to come face-to-face with Middleton, but admits her rival was "very gracious" after she broached the topic of their famous butts when they met at Buckingham Palace.

She says, "I met Pippa at the Jubilee just after I'd been on (Tv) and joked about having a better bottom then her. We said hi... We were chatting and then I just blurted out about our bums. She was very gracious and said I would win hands down but I'm not too sure about that.

"I think if there was a competition between me, Kim Kardashian and Pippa Middleton for best bum I would come third. I don't know who would win out of those two girls but I'm just hanging in there. My glory days are definitely behind me, pardon the pun."