Before & After: Celebs' Most Dramatic Transformations

The Biebs was just 13 when he first got famous, so a little growing up was to be expected. The bleach blonde comb-over, we did not see coming.

Khloe has glammed-up and slimmed down in a major way since she and her reality star sisters first broke on the scene in 2007.

A former Disney star, Cyrus has left Hannah Montana in the dust in recent years, pushing boundaries with her fashion choices and unapologetic drug use.

Everyone's favorite Jersey Shore "meatball" is all grown up now. Since her years at the shore, Polizzi has become a mother of two and a published author, recently releasing her fifth book, Strong is the New Sexy.

Lukas Haas, is that you?! The Witness actor/Leonardo DiCaprio's bestie looked unrecognizable while out and about in Beverly Hills, Calif. on Thursday, sporting a gray beard and a shoulder-length 'do. The formerly clean-shaven actor's new look is reportedly for an upcoming film with DiCaprio. "They both had to grow beards for the movie," Us Weekly quotes a source.

Renee Zellweger's new face might be the latest target of media scrutiny, but the actress is certainly not the first celebrity to drastically alter her appearance.

The Grease star was a heartthrob in his early acting days, but recent public appearances have raised eyebrows over what seems to be big changes to his hair – and a face that doesn't move.

The actress and reality star has changed more than just her hair color since her days in the 90210.

Rourke, a former boxer, admits to having reconstructive surgery. "Most of it was to mend the mess of my face because of the boxing," he said in 2009. "But I went to the wrong guy to put my face back together."

The rapper made headlines at the 1999 VMAs with her scandalous purple outfit and shocked fans again at the 2013 awards show when she stepped out with a dramatically different appearance. 

The TV star cops to having Botox and filler injections, but admitted that she overdid it with Juvéderm at one point. "You have to be careful," Rinna told In Touch Magazine in 2008. "I'm a perfect example of that!"

The actress and singer never publicly admitted to having a nose job, but dad/manager Joe Simpson copped to Fox News that "there was a real problem with her breathing and that was cured."

The actress has had many different looks throughout the years, but Kidman today looks like a completely different person compared to this shot from her early acting days in Australia!