Stearns, who played football and baseball at the University of Colorado, died Thursday night in Denver, according to the Mets.
He died less than three weeks after attending an Old Timers' Day at Citi Field in New York that coincided with the Mets' 60th anniversary. He was noticeably thin in his Mets jersey Aug. 27 and waved to the crowd when he was introduced on the field.
"No one played the game with more spirit or determination than John Stearns," Mets president Sandy Alderson said Friday in a statement. "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."