John Legend found it “an easy decision” to duet with Kelly Clarkson.

The All of Me singer teamed up with the American Idol winner on the track Run, Run, Run which features on her latest album Piece By Piece. And the Oscar winning songwriter couldn’t speak highly enough of the 32-year-old.

“Kelly's one of the best singers in the business, I think," he told ET Online. "When she reached out to me, I thought it was an easy decision. I thought the song was great and it'd be great to reunite with my old friend from Duets."

As well as working with Kelly, John also teamed up with rapper Common on Glory for the Selma soundtrack. Their efforts resulted in an Academy Award for Best Original Song earlier this year, which the 36-year-old admits has changed his life. As for who he would love to make music with next, John confesses he’s running out of options.

“There's not many people left!" he laughed. "I'm just focused on trying to make great music and whenever the collaborations come, they come, but I don't focus on who I want to work with next. It's usually about just trying to make great music."

And with this in mind, the star revealed that he is working on a follow up to his most recent album, Love in the Future.

“I'm just about to start now. I don't know exactly who I'm gonna work with yet, but as soon as I get back from a week off, which is about to happen [on Sunday], I'm gonna start writing new songs,” he added.