Justin Bieber may have been the big winner at the 40th annual American Music Awards on Sunday night in Los Angeles, California -- he took home three trophies including Artist of the Year -- but it's South Korean rapper Psy and his performance everyone is talking about Monday morning.

He had everyone in the Nokia Theater at L.A. Live on their feet and then ... things went to the next level.  Three minutes into his high energy performance, the stage goes dark, the music stops, and suddenly, it's "Hammertime!" MC Hammer appears on stage next to Psy and the two begin to tear up the stage to a mashup of MC Hammer's 1991 hit “2 Legit 2 Quit” and Psy’s "Gangnam Style." 

Judging from Eric Stonestreet’s (Cam on ABC's "Modern Family") reaction, the crowd wasn't expecting Hammer to take the stage! Watch:



If Twitter is any indication, the return of MC Hammer was a happy occasion:

and HAMMER killed it. haha

— Justin Bieber (@justinbieber) November 19, 2012

MC Hammer just shut it down!!!#AMAs

— Keshia K Pulliam (@peachespulliam) November 19, 2012

And the award for best performance goes to.......... PSY and MC Hammer!!!! How much fun was that!?!?!?

— P!nk (@Pink) November 19, 2012

Psy closing w mc hammer #toolegit instagr.am/p/SM69D1lWfk/

— Ryan Seacrest (@RyanSeacrest) November 19, 2012

The show also included a Stevie Wonder tribute to Dick Clark -- the creator and longtime producer of the American Music Awards who died last April, and performances by Pink, Kelly Clarkson and Pitbull with Christina Aguilera.

Taylor Swift also took to the stage to sing "I Knew You Were Trouble" and accept her fifth consecutive award for favorite female country artist!

For a full list of the winners, check out the American Music Awards page at ABC.com.