He was just 21 years old.

"It is we great sadness that we announce the passing of Rodion Amirov. Two years ago, Rodion was diagnosed with a brain tumour. 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," agent Daniel Milstein wrote.

Amirov was diagnosed with the tumor in February 2022 after undergoing treatment for an unrelated injury in Russia. Rodion, a left winger, spent his entire career with the Maple Leafs on loan in his native Russia ... before halting his career permanently.

Toronto signed Rodion to a three-year entry-level contract after he was selected 15th overall in the 2020 NHL Draft.

Maple Leafs president Brendan Shanahan also released a statement addressing the terrible news.

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

Shanahan continued ... "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.”

Playing on loan in the Kontinental Hockey League for Salavat Yulaev Ufa -- his hometown club -- Rodion scored one goal during the 2021-2022 season and 10 across his six-year professional career.

Rodion also played for Russia internationally and won a silver medal at the World U18 Championships.

"We will always remember his courage, his desire, his will, his smile, all of the great things about him."