Dannii Minogue has revealed the secret to her enviable toned behind is her Spanx control underwear.

The X Factor judge, who is about to give birth to her first child, told Heat magazine: “My secret? Spanx!

“I always wear them on the red carpet – they make my butt into the shape it would be if I was really good and went to the gym and had a personal trainer!”

Dannii, who is dating ex-rugby league player Kris Smith, has been trying to adjust to wearing flat shoes rather than her favourite high heels.

“At home I live in Uggs. I wore a pair of flats yesterday when I met my sister for lunch. She was like, ‘What’s going on? Wow, that’s different!'” she said.

“Apart from my flip-flops and my Ugg boots, I only own one pair of flat shoes – a little pair of Jimmy Choos.”