An anti-vaccine kickboxing champion has died from COVID-19 complications after he refused to acknowledge he was severely ill and discharged himself early from the hospital.

Frederic Sinistra, 41, known in kickboxing community as 'The Undertaker,' has died in his home in Ciney, Belgium, according to an announcement posted to his social media earlier this week.

Sinistra's death comes after he was admitted to the hospital in November at the request of his coach, according to Yahoo Sports. During his treatment, Sinistra shared photos and videos of himself inside of an intensive care unit, while maintaining that he would "come back even stronger," and telling fans he was feeling "better and better."

"I was born premature and I will continue to fight to the death like a man without ever giving up and dying without regrets," he wrote in an Instagram post.

The three-time world champion also criticized COVID-19 restrictions while in the hospital, writing that he was "disgusted" to learn that a kickboxing match scheduled for December was canceled.

Then, in late November, Sinistra decided to check himself out of the hospital early, calling COVID "the little virus," according to Yahoo Sports. At that time, the kickboxer was reportedly treating himself with oxygen at home.

The athlete succumbed to the virus via cardiac arrest nearly a month later, Fox Sports reported. His death was announced on social media by his wife on December 23.

"From the bottom of my heart thank you all for your support and all your beautiful tributes to my husband," Sinistra's wife, who has not been identified in media reports, wrote on his Facebook page. "My husband was a generous man with a big heart who wanted to help others against and against everything."

In this same post, his wife refused to admit that the anti-vax athlete died from COVID-19 complications, adding that "never would he have accepted that we used what happened to him to spread fear and call for vaccination."

"[I] will fight to the end so that the truth is restored and his name is washed away from all these slanderers both family and around his death," she added.

Anti-Vaxx Kickboxer Dies From COVID
Anti-vaccine kickboxer Frederic Sinistra has died from COVID-19 complications. Here, Sinistra is seen in a fight during the Fight Night 2018 at the Citadelle of Saint-Tropez Party On French Riviera on August 4, 2018 in Saint-Tropez, France.Foc Kan/WireImage/Getty Images

Sinistra has won several world and European heavyweight kickboxing titles throughout his 39-9 career and claimed a national title in Belgium in 2004, according to Yahoo Sports. At one point in his athletic history, the 41-year-old was even dubbed "Belgium's strongest man."

"I will never forget him," his friend, Jordan Sferrazza wrote after his death on social media, according to Yahoo Sports. "He was the strongest in Belgium in the heavyweight category."