From Carrie Underwood to Clay Aiken: 8 of the Most Jaw-Dropping Transformations From 'American Idol' Finale

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What a difference a few years and a personal stylist can make!

After 15 seasons, American Idol crowned its last winner on Thursday night's series finale, and boasted numerous performances from some of the show's most beloved alumni and the return of former judges Randy Jackson, Paula Abdul and Simon Cowell.

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Many of the show's contestants have gone on to make a name for themselves in the entertainment industry, and in doing so, have undergone fierce makeovers. Here are eight of the most shocking Idol transformations fans witnessed on last night's finale:

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1. Kellie Picker: While her style has changed, Pickler's smile is brighter than ever! The country crooner was just 20 years old when she came in sixth place on the fifth season of Idol, and she leveraged time on the show into a full-fledged music career.

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2. Justin Guarini: The curls were nowhere to be found when the season one runner-up showed up for the Idol finale. Now 37, Guarini exchanged his pleather styles and big hair that he was known for in 2002 for sleek suits and a clean-cut demeanor.

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3. Carrie Underwood: One of the most successful Idol winners, Underwood has undergone a major makeover. The 33-year-old country music star rocked not one, but three sexy styles on the show's finale, which is a far cry from the conservative boot-cut jeans and plaid shirt she wore during one of her first performances on the show in 2006.

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4. Katharine McPhee: The runner-up in 2006 was McPhee, and since then, the 32-year-old actress/singer has gone from a brunette vixen to a blonde bombshell.

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5. Clay Aiken: The 2003 runner-up put his music on the back burner to pursue politics, and that was evident when he performed on the finale in a traditional suit.

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6. Ace Young: The heartthrob of Idol's 2006 season looked just as handsome at 35 with his short hair, and was just as eager to perform on the Idol stage as he was over a decade ago.

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7. Jordin Sparks: The 2007 winner put on a sexy display when she hit the red carpet in a midriff blouse on Thursday night. The 26-year-old singer has been working on her fitness since her big win on Idol, and it certainly shows.

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8. Simon Cowell, Randy Jackson and Paula Abdul: The three original judges of the beloved series cleaned up nice for the grande finale. Cowell chose a suit over his trademark black T-shirt, while Abdul wore a classy (yet sassy) outfit. As for Jackson, he was significantly slimmer than when America was introduced to him in 2002.

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Another great moment on Idol was when the show's first winner, Kelly Clarkson, performed a beautiful, emotional medley. Check out this flashback video to see how far she's come:

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