In the photo, which is from The Christmas Chronicles, Hawn dons her most festive gear and sits next to Russell, who plays a modernized version of Santa.
"Never thought I'd be sleeping with Santa!" Hawn captioned the image.
"Best Part of the movie !!" commented Reese Witherspoon.
"I dont believe that," comedian Amy Schumer said.
"This made my year," wrote Josh Gad.
"Name a more iconic duo...I'll wait," wrote the movie's official Instagram profile.
Hawn isn't the only familial connection in the new movie. Her son, Oliver Hudson, who she shares with musician Bill Hudson and who was raised with sister Kate Hudson by Russell, plays the late father to the film's two lead child actors, Teddy (Judah Lewis) and Kate (Darby Camp). Hudson appears mostly in old family videos as his character's children celebrate their first Christmas since losing their dad.
What makes the movie even more special is that the couple's 7-year-old grandson Bing Bellamy — Kate Hudson's son with Muse frontman Matt Bellamy — also briefly appears as a kid sending a wish-list video to Santa. Both Bing's name and the name of his 14-year-old brother Ryder Robinson are called out later during a montage where Santa Claus (Russell) delivers presents.
Nearly the entire family celebrated the movie's premiere in Los Angeles a few days before Thanksgiving. Russell and Hawn, who have been together since 1983, were joined by Oliver Hudson and his wife Erin Bartlett and their three kids, sons Wilder Brooks, 11, and Bodhi Hawn, 8, and daughter Rio, 5.0comments
Bing also made an appearance with his uncle Wyatt Russell, who is the son of Hawn and Russell, as well as Wyatt's girlfriend Meredith Hagner. Kate Hudson stayed home with Ryder and her newborn with boyfriend Danny Fujikawa, Rani Rose.
The Christmas Chronicles is available to stream now on Netflix.