And then, just two days later, he wasn't.

The Checkers were kings of the American Hockey League, and Stelio Mattheos was on top of the world.

"The words we've been waiting to say for so long … for the first time in franchise history, the Charlotte Checkers are Calder Cup champions!" Jason Shaya's radio play-by-play call was raw and emotional as celebratory pandemonium ensued on the ice in Rosemont, Ill., on June 8.

***

Mattheos, then 19, joined the Checkers in March following the conclusion of his third season with the Brandon Wheat Kings, in which he ranked fourth in the Western Hockey League in goals (44) and sixth in points (96).

He played in 11 games for Charlotte down the stretch of the regular season and recorded a pair of goals and an assist. He skated in another 14 games in the Calder Cup Playoffs, registering three goals and one assist.

"It was fantastic. We had a great team," Mattheos said. "I had an unbelievable time going there and joining the team late. We ended up winning, and it was crazy."

But, there were a few nagging concerns. Mattheos experienced some pain while walking in the airport during the finals. During the morning skate prior to the decisive Game 5, he found himself short of breath.

"Something didn't feel right," he recalled. "I kind of knew something was up."

The Checkers hosted a championship celebration in Charlotte on June 10. Mattheos put on a brave face and a smile, but behind closed locker room doors, he had news to share with his teammates.

***

The doctors first informed Mattheos that he wouldn't be able to play hockey for a few months.

"I didn't know exactly why, but I remember being upset," he said.

Two days after winning the Calder Cup and four days prior to his 20th birthday, Mattheos was diagnosed with testicular cancer.

"Just, shock," he said. "Fear for a bit, too. It's a scary word."

Mattheos was alone at the doctor's office but, as soon as he walked out of the door, he called his family.

"You're just thinking about life and everything. It's just a really scary word to hear," he said. "To be honest, I don't even remember exactly what I was thinking. It just happened really fast."

Not even 48 hours separated one of the best moments of Mattheos' life from one of the scariest.

"It kind of put everything into perspective," he said. "It's not just about hockey. It's about life."

***

Vegas Golden Knights defenseman Shea Theodore, in an essay for The Players' Tribune, said "everything was really a blur" when he received the same diagnosis.

Mattheos concurred. One night he was playing in the Calder Cup Finals, and soon after, hockey became one of his least concerns. After consulting with physicians, Mattheos flew home to Winnipeg and underwent surgery to remove one testicle.

Three rounds of chemotherapy followed over the course of the summer, but the good news was that Mattheos was expected to return to full health.

"It was a big grind, for sure, and some very tough weeks. I wasn't feeling my best," he said. "I'm sitting in the chair, IV hooked up to me, wasn't really able to walk around or anything. I was there for 10 hours a day when I was in treatment. Seeing older people in there, talking to them, getting treatment with them, they were telling me they'd been doing this for decades or people telling me their cancer wasn't curable. It really put things into perspective that I was one of the lucky ones in there, for sure."

Mattheos tried to remain active when he could, getting in the gym or hitting the ice for a light skate.

"It didn't feel like work. I just wanted to get out of the house," he said. "The drugs kill your red blood cells in your body, and still they're not all back, and I remember in the gym older people flying past me. I was just like, 'Wow, I've got a long way to go.'"

And through it all, his teammates remained in touch, supporting him every step of the way.

"I really appreciated that throughout the whole thing," he said. "It shows how much character everyone has here."

"There are really no words to describe that, right? It's a fight that relates to everyone," said Haydn Fleury, who roomed with Mattheos during the Calder Cup Finals. "He wasn't alone in the process, and he's a young kid who has a bright future ahead of him."

***

On Friday, Sept. 20, a week into Carolina Hurricanes' training camp, the north-side doors of the locker room opened, and Mattheos walked in, his hockey bag and sticks in tow.

His Checkers teammates were the first to spot him. Fleury embraced him. So, too, did Julien Gauthier.

"Really cool. Really happy for him," Fleury recalled of the moment. "He fought all summer. It was good to see him in training camp."

The next morning, Mattheos laced up his skates and got on the PNC Arena ice.

"To get clearance and get back to doing what I love is an amazing feeling. It's great to see all my friends and my teammates here," he smiled. "I'm just excited to put this behind me and play hockey again."

Mattheos completed his comeback to hockey in early November, returning to the Checkers' lineup for a weekend set in Cleveland.

His story, though, is still only beginning.

Mattheos, selected by the Canes in the third round of the 2017 NHL Draft, aspires to one day play in the National Hockey League, of course. And as Hockey Fights Cancer, so too will Mattheos continue his fight, having already conquered one of life's biggest hurdles this past summer.

"I just want to be known as a hockey player, a good guy who plays hockey. It's a huge part of my life. It was scary for a little while because I didn't know what exactly the future was going to hold, but now I'm excited to be back," he said. "I'm not going to doubt myself. I've made it this far. I know it's going to be tough, but I'm not going to give up."

Video: Stelio's Fight