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PSY and MC Hammer don Hammer pants to rock the AMAs with 'Gangnam Style'

Nostalgia rang throughout Sunday night's American Music Awards, as the show celebrated its 40th anniversary with clips from past shows and other looks back. But the retro vibe was never louder than in the show's final act, when South Korean viral sensation PSY and 1980s-1990s rapper MC Hammer shared a stage -- and a fashion sense -- to perform PSY's hit, "Gangnam Style."

Danny Moloshok / Reuters

South Korean rapper Psy performs "Gangnam Style" with MC Hammer at the AMAs.

Dressed all in black, PSY took the stage first, sporting a version of the baggy "Hammer pants" MC Hammer made famous decades ago. Then MC Hammer himself joined in, though his outfit was all in white.

The billowy trousers didn't stop either musician from dancing up a storm, even trotting through the famed horse-riding style dance PSY tackles in the "Gangnam" video.

Christopher Polk / Getty Images

Singer Justin Bieber wore MC Hammer-style pants to the AMAs.

Hammer wasn't the only nostalgic act to take the AMA stage. Boy banders The Backstreet Boys, who celebrate their 20th anniversary next year, also made an appearance.

Jason Merritt / Getty Images

Singer Justin Bieber's striking shoes.

In contrast, the night's big winner, Canadian teen singer Justin Bieber, wasn't born until 1994, at which point the Backstreet Boys and MC Hammer were already well into their fame. Yet even Bieber himself sported a version of Hammer's baggy pants, along with a fashion twist of his own -- what appeared to be red slip-on shoes dotted with tiny black spikes. No one step on his foot!

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