Have mercy!

John Stamos, 51, took to Instagram on Sunday to show off his chiseled abs in a shirtless selfie. 

"51 no filters F' it," he captioned the sexy bathroom snapshot.

The former "Full House" hunk works hard to stay in shape, revealing that he gets beach-ready with Pilates classes.

"I go in and it’s all women except for me," he told Life & Style last year. "I’m the only guy there, and I know they make up these exercises like ‘come over here, John, and do the penguin.’ And then it looks like I’m getting a pap smear. They do it to make me look silly, but it keeps me in shape."

He doesn't care that it's all women in his classes, and we're willing to bet the women don't care either!

What do you think of his shirtless selfie? Tell toofab in the comment section below, and click "Launch Gallery" above to see more sexy stars.

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