Will.i.am has reflected on his surprise appearance during Usher's Super Bowl Halftime Show on Sunday.

The Black Eyed Peas frontman took to the stage at the Allegiant Stadium in Las Vegas as Usher's guest star, 13 years after Usher appeared as Will's guest star during the 2011 Super Bowl.

"How can I explain it? There's no words to really explain that," the performer told The Hollywood Reporter after the event. "Now 13 years later, it means something totally different. It's beautiful. It was wonderful. It's fantastic."

Will also raved about Usher's performance, which included dancers roller-skating and doing tricks on stage.

"The reason I say our section was the most 'What the F?' is because we've never seen roller skating at any type of big world stage like that," the Scream & Shout hitmaker said. "It felt like the urban Olympics. He brought the urban Olympics to the Super Bowl."

Will added that the show, which featured 13 minutes of Usher's hits, had a "lot of OMG moments... so many OMG moments that 60 seconds of OMG was all you needed because the show was 'oh my gosh.'"

Will joined Usher to perform their 2010 hit song, OMG. They performed the same track during the 2011 Halftime Show.

Usher was also joined on stage by Ludacris, Lil Jon, Alicia Keys and H.E.R.