Former Mets exec Randye Ringler announced the news on his social media page ... saying Stearns -- who played for NY from 1975 to 1984 -- passed away on Thursday.

"May he be setting up to catch Tom Seaver in Baseball Heaven and Resting in Peace," Ringler said. "He left us all with so many wonderful memories."

A cause of death was not revealed ... but Stearns had been battling prostate cancer.

"No one played the game with more spirit or determination than John Stearns," Mets president Sandy Alderson said Friday morning. "He literally willed himself to attend Old Timers' Day last month so he could visit friends and old teammates."

"Despite his illness, he even managed to step into the batting cage to take a few swings. His nickname, 'Bad Dude' couldn’t have been more appropriate. A four-time All Star, John was one of the most complete catchers in Mets history. Our thoughts and prayers are with his friends and family."

Stearns started his career in the show with the Philadelphia Phillies in 1974 -- but only played one game before he was traded to the Mets.

He went on to become a fan favorite for the way he played behind the dish. In one of his most memorable moments as a catcher, he broke Pirates outfielder Dave Parkers' cheekbone after he tagged him to end a game in 1978.

Stearns' most famous moment, though, came in 1980 ... when he subdued a fan who ran onto the playing field. Stearns also gained notoriety for his involvement in a bench-clearing brawl weeks later.

After retirement, due to career-ending injuries, Stearns held several roles in the league including being a scout for the Mets, Brewers and Reds.

He also became an ESPN broadcaster in 1993.