Stefani's personal life is off-limits, the BBC is told in advance of this interview - but she happily chats away about Shelton, after pausing to check whether we've heard of him. We definitely have. After all, he's just been named the sexiest man alive.

"Exactly!" Stefani laughs, with a self-deprecating flick of her hair. "I don't know if you heard about him? The sexiest man alive? That's my boyfriend, by the way."

In fact, it was going to be hard to avoid discussing Shelton, since he co-wrote the title track on You Make It Feel Like Christmas, a cute little love song that rides the rhythm of The Supremes' You Can't Hurry Love.

The track came out of the blue, says Stefani, as Shelton has largely given up writing his own songs. "He went to Nashville just to be a writer but he doesn't enjoy it, I guess. He just likes singing," she explains. "But he just happened to be sitting around on the [tour] bus and started writing that song, You Make It Feel Like Christmas. He sent me a voice text and I was like, 'I was just thinking about your record and I don't know if this is any good'. And I was like, 'Oh my gosh, this sounds like a hit!' It's one thing to write a Christmas song that's mid-tempo or slow or emotional, but an uptempo, fun, joyful one? That's hard."