The 46-year-old actress recently appeared on The Tonight Show Starring Jimmy Fallon, where she revealed that she's convinced that she and the Deadpool star are look-alikes.
On Monday, Reynolds, 43, responded by posting the poster for Double, Double, Toil and Trouble, the 1993 Halloween-themed movie starring Mary-Kate and Ashley Olsen, except his and Beckinsale's faces are crudely photoshopped over the former child stars.
"F**k it. We already have a script," Reynolds hilariously wrote alongside the pic.
While on the Tonight Show, Beckinsale admitted that sometimes, when she sees an advertisement for a project starring Reynolds, she momentarily mistakes him for herself.
"I look exactly like Ryan Reynolds," Beckinsale argued. "Like in a shocking way. Like, when sometimes I see a bus going by with a poster on it, I think, 'Damn, I look hot. Oh, wait, that's not me. Also, I never did that movie.'"
The leading lady added: "I've wrestled with how, obviously, he's not even, like, a sort of slightly girly, boy-bander type. He's, like, a big Canadian man and I really see myself in him."
And, if on the off chance Reynolds would really be willing to team up with Beckinsale for a project, she shut down the possibility in a hurry, stating, "I can't be in the same room as him because one of us, I think, would explode or something would happen."