After deciding to record a new Christmas album, A Holly Dolly Christmas, with a bunch of friends, Dolly knew she had to record her favourite festive tune - and she asked Willie to join her for a duet.

"I could not do a Christmas album at this time without doing this song," Parton explained, Taste of Country reported.

She recalled Nelson responded just as an old friend would: "Aw, hell, you think you gotta ask me that? Of course I'm gonna sing a duet with you on it."

Nelson wrote the track in the early 1960s and it became a big hit for the late Roy Orbison.

Dolly insisted it's a very important song to her: "Christmas is about giving and caring and paying attention," she said.

"It's (song) sad, but it's beautifully done and beautifully written, and it's very singable, too, and it just paints such a picture. Willie's a great writer," the star mused.

The pair has released an animated video to accompany the new version of the song.