President Obama watched Psy perform at the 'Christmas in Washington' charity concert on Sunday night and shook hands with the South Korean pop star, despite the controversy surrounding his 2004 performance of a song that called for killing “Yankees” in Iraq.

Eight years ago, Psy, born Park Jae-sang, participated in a concert where he sang a song called 'Dear American,' penned by the South Korean rock band N.E.X.T. The antiwar tune calls for the death of “Yankees” that were involved in torture. The lyrics state: “Kill their daughters, mothers, daughters-in-law and fathers, kill them all slowly and painfully.”

In a statement on Friday, the artist apologized for his "inflammatory and inappropriate language." "I will forever be sorry for any pain I have caused by those words,” he wrote. “While I'm grateful for the freedom to express one's self, I've learned there are limits to what language is appropriate and I'm deeply sorry for how these lyrics could be interpreted.”

According to the L.A. Times, Psy has since performed in front of U.S. service members, praising them for their work and sacrifice. He added in the statement, “In my music, I try to give people a release, a reason to smile. I have learned that through music, our universal language, we can all come together as a culture of humanity and I hope that you will accept my apology.”

Although Obama made a speech at the 'Christmas in Washington' event, he did not mention Psy. The concert, which raises money for the Children's National Medical Center in Washington, will be broadcast on Friday, Dec. 21 on TNT.

Watch the Psy 'Gangnam Style' Video