Toronto Maple Leafs forward prospect Rodion Amirov, the club's 2020 first-round pick, has died, his agent, Dan Milstein, confirmed Monday. He was 21.

Milstein posted on X, formerly known as Twitter, that Amirov died after being diagnosed with a brain tumor.

"From the moment he received the news, he refused to speak in the negative, determined to enjoy every day, facing it with the same positive attitude he showed during his hockey career," Milstein said in a statement. "We will always remember his courage, his desire, his will, his smile, all of the great things about him."

Milstein said in the statement that Amirov had been diagnosed with the brain tumor two years ago. The Maple Leafs announced Amirov's diagnosis in February 2022.

Amirov, who was the 15th pick in 2020, signed an entry-level contract with the Maple Leafs in April 2021. He joined the Maple Leafs' taxi squad that spring after finishing a KHL campaign with Salavet Yulaev Ufa. He scored nine goals and 13 points in 39 games as a teenager.

He returned to Russia for another campaign before sustaining an injury before the start of the KHL season. Amirov missed his team's first eight games and returned to the lineup by late September only to sustain another injury.

At the time, Ufa coach Tomi Lamsa did not provide specifics regarding Amirov's injury. He would not play for nearly two months. Amirov was assigned to UFA's minor league team in the VHL in November. He played three games before returning to the KHL in early December.

While he was back in the KHL, Amirov received minimal ice time. He logged two shifts in his first game back and was listed as a healthy scratch in the next game. Amirov would work his way back and was logging close to 10 minutes per game before testing positive for COVID-19, which derailed his progress.

When the Leafs announced Amirov's diagnosis, the team stated he sustained an injury during the 2021-22 season while playing in the KHL. While Amirov was recovering, he developed "new, unrelated symptoms that required ongoing extensive investigations over the last few months."

Amirov played only 10 KHL games that season as he went to a medical facility in Germany for treatment.

Milstein thanked Amirov's doctors, the Maple Leafs and Salavat Yulayev Ufa for what they did to help Amirov and his family. Milstein also thanked hockey fans who reached out in support of Amirov and his family.

Maple Leafs president and alternate governor Brendan Shanahan issued a statement shortly after Milstein announced Amirov had died.

"The entire Maple Leafs organization is devastated by this tragic loss," Shanahan said. "Over the duration of his courageous battle, Rodion's positivity inspired everyone around him, and he made lasting impressions with our team and our fans in his brief visits to Toronto.

"It's incredibly sad to see a young man with so much promise taken from us so soon. We offer our deepest condolences to Rodion's family and friends as we mourn this loss together."