Kate Beckinsale sent pornographic photos featuring her own face to her mother.
The 'Only Living Boy in New York' star was horrified to stumble across her own likeness superimposed on some explicit pictures, but decided to share them with her mum to find out how she'd respond - and was even more shocked when her parent "offensively" thought they were really her at first.
She told talk show host Jimmy Kimmel: "I know Reddit is the one where sometimes you can find pictures of porn stars with your own face on it.
"I've been sent a few very distressing photos of myself--very busy, actually. Not just sort of in a wicker chair, naked--but involved. You know what I mean? With more than one person.
"So, when I got sent it, I just immediately sent it to my mother with no explanation to see what would happen.
"She's used to shocks, but, really offensively, I get a text back going, 'Oh, darling! Oh, dear! Oh, no! Oh, phew! You've got hardwood floors and that's a carpet.'
"It was, 'Oh, my God! What can I possibly cling onto that proves this isn't Kate?' Not my six African American boyfriends - all at once - but the fact that that's a carpet."
The 44-year-old actress also used her appearance on the show to embarrass both the host and her 18-year-old daughter Lily - who she has with former partner Michael Sheen - by revealing the teenager has a crush on Jimmy.
And Kate admitted the situation is all the more "twisted" because Jimmy used to date Michael's current partner Sarah Silverman.
She said: "You know how they have crushes on Justin Bieber and things like that? She's got one on you.
"It's a little bit of a tricky situation, because my daughter's dad is dating Jimmy's ex-girlfriend--it's very twisted. It's a sort of horrible, 'Human Centipede'-y vibe.
"Anyway, I think you should be pleased. She's very attractive... She's out of your league! I just want you to know that."
The 49-year-old presenter - who has two grown-up children with first wife Gina Maddy and daughter Jane, three, and son Billy, three months, with spouse Molly McNearney - admitted he was "flattered" by Lily's attention.
Speaking directly to the teenager - who was in the audience - he said: "I'm sorry! I had nothing to do with this! This is all her! This is your mother! Let's not ruin the crush thing."
"I want to keep that going, OK? Thank you very much. I appreciate it. I'm flattered. [Now] we're both embarrassed."