Gwen Stefani Reveals How Her Love Song with Blake Shelton Was Born!

"The Voice" coaches Gwen Stefani and John Legend are ready for Christmas!

"Extra's" Renee Bargh joined the coaches on the set of the show, where Gwen explained, "It's Christmas, it's time to celebrate."

She's also celebrating her new love song with boyfriend Blake Shelton, "Nobody but You."

Stefani revealed how it came about, saying, "Neither one of us wrote this song. It came to us, and when Blake heard it we were working out in the gym. He's playing the song and I'm like, 'You are such a f--king a--hole. Everybody sings these incredible songs.' I am thinking in my brain, and I was like, 'God, I wish I was on this song…' and he turns and says, 'God, I wish you were on this song,' and I was like, 'I was just thinking that!' And he's like, 'I was just thinking that! You have to be on this song.' That's kind of how it happened."

Stefani's advance hype worked in real time, with Legend insisting, "I'm dying to hear this song."

Meanwhile, John said he and his family are so ready for Christmas. "Luna is excited," he said of his 3-year-old daughter with Chrissy Teigen. "She's making her list."

The coaches, however, are not so ready for the finals of "The Voice." John said, "So much is nerve-wracking about this show… I can't imagine going through this like a young person… It's crazy to watch."

Gwen added, "I felt nervous waking up this morning! I had to get some prayer going… I really want Rose [Short] to win."