Former UFC star Anthony Johnson reportedly died from organ failure due to a bout with non-Hodgkin’s lymphoma and hemophagocytic lymphohistiocytosis. He was 38.

Johnson’s death was announced on Sunday in a statement from Bellator MMA, the last promotion that former light heavyweight title contender competed in. Yahoo Sports reported the cause of death.

The young mixed martial artist had been ill for more than a year, a Bellator spokesperson told the Associated Press. But he wasn’t known for speaking out about what was plaguing him.

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Anthony Johnson fights Alexander Gustafsson

Anthony 'Rumble' Johnson (L) of the U.S. fights with Alexander 'The Mauler' Gustafsson of Sweden in their UFC light heavyweight mixed martial arts bout at Tele2 Arena in Stockholm January 24, 2015. (REUTERS/Jessica Gow/TT News Agency)

Kamaru Usman told Yahoo Sports he talked to Johnson a few months ago but didn’t have the details about what was going on with him.

"You know, it was a little like Chadwick Boseman," Usman said. "Chadwick kept his issue private, and we were all so shocked and surprised [when he died in 2020]. Rumble would give you these nonchalant stories, and he was having dialysis on his kidneys, but he never really told you fully what was going on. He didn't want to be treated differently. He didn't want people seeing him losing all this weight and going through these situations and treat him differently because of what was going on. He was such an incredible athlete.

"He had the feet of a welterweight and the power of a heavyweight, and he was able to transfer that throughout his career. He was truly special and gifted, and he didn't really have to try hard. He felt he was working hard, but there were levels he didn't go to, maybe didn't want to go to. He was natural. I admired that so much. He made it look easy. He'd hit a guy and the guy would just crumble. I mean, I worked so hard and put this time in, and I'd wind up and hit this guy with everything, and he'd be standing there. Rumble was a different caliber than the rest of us."

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Johnson posted a worrying message in September 2021 that he needed "as many prayers as I can get" and was in a battle that wasn’t COVID-19 related. Johnson then posted in May that he received information from a doctor that he had made "big improvements."

Anthony Johnson in Buffalo

Anthony Johnson enters the arena prior to the Ligh Heavyweight Title Bout against Daniel Cormier at KeyBank Center on April 8, 2017 in Buffalo, New York.  (Mike Roach/Zuffa LLC/Zuffa LLC via Getty Images)

In October, Johnson’s manager told ESPN that "Rumble" was "going through some health problems right now. … He’s not doing well."

Daniel Cormier, whom Johnson had a major rivalry with, was among those who paid tribute to "Rumble."

"Rest Easy my brother. For a guy who struck fear in so many peoples heart Anthony Johnson was a caring person," Cormier tweeted. "From random text to check ins during loss. What a person he was, Rumble will be missed. Sometimes life doesn’t seem fair. Horrible news."

Johnson had 11 knockouts during his decade in UFC. He fought from 2007 to 2017 and lost twice to Cormier in light heavyweight title bouts. He competed in three weight classes during his time at UFC and became one of the most powerful punchers the company had ever seen.

Anthony Johnson retires

Anthony Johnson announces his retirement after his defeat to Daniel Cormier in their UFC light heavyweight championship bout during the UFC 210 event at KeyBank Center on April 8, 2017 in Buffalo, New York. (Josh Hedges/Zuffa LLC/Zuffa LLC via Getty Images)

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He retired from UFC in 2017 and was competing in Bellator in 2021 before his health problems worsened.

The Associated Press contributed to this report.