The stars play an unlikely superhero couple in the new Disney+ series, which debuts on Friday, January 15, and during a TV interview earlier this week Olsen went public with the embarrassing moment, revealing it really made Bettany mad when she pointed it out.
But appearing on the same show, "Good Morning America", on Wednesday, the Brit insisted the snot was Olsen's - not his.
"(It's a) gross miscarriage of justice," he said. "During a kissing scene... snot appeared on both our lips, which is of course disgusting. I was a gentleman and kinda went away and pretended it didn't happen and she, rather grumpily, pointed the finger at me."
"I can prove categorically it was her snot, not my snot... If Elizabeth 'Snotter' Olsen - as I call her - were here today, she would be the first to tell you when she gets emotional in a scene her nose runs before the tears come, whereas I'm English... and unable to express emotion."
Both stars, who have appeared in countless Marvel movies, have made it clear their outrage is just a fun line to help promote the new series.
In related news, Marvel boss Kevin Feige reacted to people calling the half-hour sitcom weird, at least compared to other Marvel shows. "Weird is good," he said. "I like weird. After 'Endgame', after the completion of a 23-movie Infinity Saga, we were soul-searching about what was coming next. 'WandaVision' being our first for Disney+ is perfect. It was always about pushing the boundaries of storytelling, doing something we could only do with the narrative structure of television."