Stefani, 49, released a video Tuesday for her single "You Make It Feel Like Christmas" featuring Shelton.
The video shows Stefani and Shelton driving home with a Christmas tree, building snowmen and performing other holiday activities. Stefani wears a number of retro-inspired looks, including one reminiscent of Marilyn Monroe.
"Check out the #YouMakeItFeelLikeChristmas video @BlakeShelton," she wrote on Instagram. "#cantbelivethishappened?!!! #christmas #music #love."
"You Make It Feel Like Christmas" appears on Stefani's holiday album of the same name, which debuted in October 2017. Stefani released a deluxe version of the album in October.
Stefani and Shelton confirmed their relationship in November 2015 following their respective splits from Gavin Rossdale and Miranda Lambert. Shelton said in an interview with Today in June that he feels closer to Stefani every day.
"Now here we are, going on three years later and every day that goes by, it just feels like a stronger bond between the two of us," the star said.
"It constantly feels like it's going to the next level. That's only way I think either of us could probably describe it," he added.