'Gangnam Style' iHeartRadio Music Festival Craze: Psy takes Las Vegas by Surprise [VIDEO]

"Gangnam Style" singer Psy made a surprising appearance at the iHeartRadio Music Festival in Las Vegas Friday putting the audience to dance to the popular horse riding choreography.

Psy appeared at the MGM Grand Arena in Las Vegas with a smile on his face and his signature slicked back hair. He was wearing a white suit with shiny lapels and sunglasses.

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His performance was not part of the official lineup.

"From now on, make some noise, come on!" the South Korean rapper shouted to the thousands in the audience, this time performing without backup dancers.

This is Psy's second big appearance at a major music event in the United States. He appeared early September in the MTV Video Music Awards 2012.

Psy's hit "Gangnam Style" went viral on YouTube. The song's music video which features the famous horse riding choreography has more than 244 million views as of today.

The iHeartRadio music festival kicked off Friday with performances by Bon Jovi, Green Day, No Doubt, Usher and Rihanna, among others.

The music festival continues today and it's been live broadcast by hundreds of Clear Channel stations across the U.S.

The website iHeartRadio also has a video live streaming available for people.

Watch Psy Perform "Gangnam Style" at the iHeartRadio Music Festival Below: