It's always a bit jarring when a celebrity's sibling goes from being cute to really, really hot. Such is the case for these celeb brothers.
RELATED: They're All Grown Up! See What Celebrities' Younger Siblings Look Like Now
Click through the gallery to see Taylor Swift, Zac Efron, and more stars' siblings transform right before your eyes.
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Emma Watson and her younger brother Josh in 2007.
Click to the next slide to see what he looks like now.
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Alex now.
He's 24-years-old.
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Blake Lively's little brother Eric in 2001.
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Eric today.
He's 35-year-old.
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Miley Cyrus and her younger brother Braison in 2007.
Click to the next slide to see what he looks like now.
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Braison now.
He's 22-years-old.
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Taylor Swift and her younger brother Austin in 2009.
Click to the next slide to see what he looks like now.
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Austin now.
He's 24-years-old.
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Lauren Conrad with her little brother Brandon in 2008.
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Brandon today.
He's 24-years-old.
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Jessica Alba and her younger brother Josh in 2001.
Click to the next slide to see what he looks like now.
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Josh now.
He's 34-years-old.
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Kate Hudson and her older brother Oliver in 1999.
Click to the next slide to see what he looks like now.
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Oliver now.
He's 40-years-old.
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Penelope Cruz with her younger sister Monica in 2006.
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Monica now.
She's 39-years-old.
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Zac Efron and his younger brother Dylan in 2011.
Click to the next slide to see what he looks like now.
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Dylan now.
He's 25-years-old.