The photo shows Ontario resident Elfriede Wolf firmly clasping Mr Clooney's hand while cupping his chiselled chin and looking into his eyes.
Ms Wolf tells Canada's Global News her daughter Brigitte is "in love" with the heartthrob. So, as the actor walked past her, she decided to yell out, "George, my daughter is in love with you."
Ms Wolf says a startled Mr Clooney replied with an "Oh my God."
He then smiled and reached over to clasp her hand. That's when she grabbed his chin.
"He is very handsome," she tells the BBC. "It was over in a moment, I was just so, so taken by that."
The photo, taken by a TIFF photographer, was posted on TIFF's official Twitter account with the caption: "FYI: Your Nonna found George and told him he wasn't eating enough." Nonna is the Italian word for grandmother.
"That's adorable," tweeted one person. "Even George knows real Nonnas squeeze faces! Good for both of them," tweeted another.
On Reddit, people had plenty of fun with the viral photo. Take a look:
Mr Clooney was at the film festival to promote his latest film, Suburbicon.
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