Kelly Clarkson reveals song she wrote the fastest

Kelly Clarkson is spilling the beans on a shocking fact about one of her chart-hitting songs.

The singer recently recalled how her song Underneath the Tree, which she produced with music producer Greg Kurstin, happens to be her fastest-written song.

"I was working with Greg Kurstin in the studio,” the three-time Grammy winner recalled in an Ask Kelly Anything video from the June 12 episode of The Kelly Clarkson Show.

“I ordered sushi and when it arrived I had written it,” the daytime talk show host revealed on the show.

“I think because I really love Christmas I write them really quickly for Christmas — because they feel good, because you can be a little cheesy, you know? You don’t have to worry about being cool, which honestly that’s not a concern generally ever because I’m not.”

That Christmas song turned out to be a huge hit for Clarkson, peaking at No. 9 on the Billboard’s Hot 100 singles chart.

It also topped Billboard's Adult Contemporary chart, holding the pinnacle position for four weeks.

Clarkson further spoke of the creative process behind its melody, saying Kurstin, 56, “sent me home with a little piano thing and we kind of started, not the idea of it, but just kind of the wall of sound for Christmas.”

She added that “it's a really cool sound at Christmas. It feels nostalgic.”

“They don’t all come out like that, though; usually it takes forever,” Clarkson admitted of her songwriting process. “But that one was quick.”