Matt Damon's advice to Josh Hartnett while filming 'Oppenheimer' was ‘so unhelpful’

Matt Damon had some advice for his fellow "Oppenheimer" star Josh Hartnett, but apparently it came a little too late.

Hartnett appeared on "The Tonight Show Starring Jimmy Fallon" earlier this week, laughing at Damon’s "unhelpful" suggestion.

"He gave me a lot of good advice," Hartnett said. "One in particular — one thing that was just so unhelpful: He told me not to gain the weight I’d already gained for the role."

He continued, "I gained about 30 pounds for the role, and he was like...