In honor of Flashback Friday, we thought it'd be fun to look back at childhood pics of some of the hottest guys in young Hollywood. It turns out that a few of our favorite heartthrobs, like Austin Mahone and Niall Horan, were a whole lot nerdier looking back when they were younger. Who knew?!

Click through to see the shocking transformations, then let us know who you think looked most nerd-tastic (we love nerdy guys!) in the comments below.

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