Kelly has rarely spent a moment out of the spotlight since her dramatic transformation. And it's not just her super-slim body that is barely recognisable but her signature style which has done a dramatic u-turn from grunge to glam. Never seen with the same hairstyle twice, the teen rebel has grown up to become one of the most celebrated style chameleons of the moment.
Ms O', who recently posed in a red bikini on the cover of Shape magazine, attributes her transformation and newfound confidence to her dance partner on Dancing With the Stars, Louis Van Amstel.
Hudson, whose drastic weight loss began after the birth of her first child, went on to become the spokeswoman for WeightWatchers.
The superslim stars were named as having the best celebrity bodies by Fitness magazine. Kate Middleton was named as Best Bride to Be for working out at the gym every day (oh, to have that time on your hands). And voluptuous Christina Hendricks was unsurprisingly top of the celebrities with curves.
Which celebrity do you think has the best body? Leave a comment in the box below and tell us your thoughts.