Story highlights Tennessee high school football player Jonathan Fluker died Monday after battling cancer

Nicknamed Superman, he wore a Superman T-shirt under his tuxedo to prom in 2014

Morristown West High School students dressed as Superman filled stands of football game

(CNN) Jonathan Fluker's best friend started calling him Superman after he was diagnosed with cancer in 2009.

Fluker was just 11 years old when doctors discovered a peripheral nerve sheath tumor. But the Tennessee teen never let it be his kryptonite, eventually going on to play on the defensive line for Morristown West High School's beloved Trojans football team, friend Lyric McCaroll said.

"He never stopped smiling and he never stopped putting a smile on my face. Even when I was full of negativity, he would reassure me that he was never going to leave me," the 17-year-old told CNN.

"I said to him 'You're my Superman, you're always going to be my Superman because you have the strength to get through this. I know you'll keep fighting and you won't give up.' "

The nickname caught on at school. Living up to the name, he wore a Superman T-shirt under his tuxedo to prom in 2014, attending in a motorized wheelchair thanks to a specially equipped van provided by the local Children's Hospital.

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