The 36-year-old singer – who has famously battled with his weight throughout his career – insists his new toned physique is all down to bedroom antics with fiancee Ayda Field.

When questioned about his new buff body, Robbie said: 'You're talking abut sex now. Yes we do it, we do it, we really do it!'

However, it isn't just sex that keeps him slim – the 'Bodies' singer also finds the time to run every day – and has used his celebrity-filled Soccer Aid charity event, which takes place on Sunday (06.06.10) as a target for getting fitter.

He told the Daily Star newspaper: 'I've been running six or seven miles a day, playing a couple of 90 minute games a week, so I am knackered.

'I don't think I've lost weight but I have toned up. It's been a good process and it's been great to have something to aim for.'

Robbie isn't the only celebrity who uses to sex to look good – 'Shrek Forever After' star Cameron Diaz also credits it as keeping her youthful.

The 37-year-old beauty said: 'I don't want to look 25 again. The fountain of youth for me, let's see. I guess it's exercise, healthy diet, lots of water, lots of laughter, lots of sex - yes, sex, we need that as human beings. It's healthy, it's natural, it's what we are here to do!"