The 45-year-old actress shared a photo of herself and Sheen, 49, on Instagram Thursday night in which the actor wore a white bunny onesie while the actress snuggled against him on the couch.
While the two exes looked comfortable, Beckinsale gave a comical explanation for why Sheen was wearing a onesie.
“So apparently there are two meanings of the word ‘perineum,’ one being the area of the body between the genitals and anus, and the other, the period of time between Christmas and New Year’s Day,” she explained in the caption.
She added, “I thought I had been clear we were celebrating the second but Michael turned up in an impenetrable onesie just in case he was ambushed by an excitable relative.”
The two actors met in 1995 while they were both in a touring production of The Seagull. The two separated in 2003 after filming Underworld. They have a 19-year-old daughter Lily Mo Sheen.
Sheen and Beckinsale have remained close since their separation. The pair spent Christmas together with their daughter and friends.
In July, Beckinsale celebrated her 45th birthday with Sheen and their daughter during a session of goat yoga.
In the gallery of photos Beckinsale shared, Sheen can be seen practicing a downward dog pose while a goat stands on his back.
In August 2017, she opened up about co-parenting with Sheen while on Chelsea with Chelsea Handler.
“I think the thing is, if you both really put your kid’s well-being first and share a sense of humor, you’re sort of halfway there,” she said.
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While the two have remained friends, they’ve also moved on. Beckinsale was seen kissing comedian Jack Whitehall in Los Angeles as they enjoyed an evening at a karaoke bar in November.
She was previously married to her Underworld director Len Wiseman for 11 years before their divorce in 2015.
Sheen split from comedian Sarah Silverman earlier this year after first being linked together in 2014.