We can now reveal the cause of death for former UFC contender Anthony “Rumble” Johnson, who tragically passed on Sunday morning at just 38 years old.

For over a year, Johnson and those close to him had hinted at extremely serious health issues that had not only kept him from competing for Bellator but were potentially life-threatening. Earlier in October, Johnson’s manager called on MMA fans to pray for “Rumble.”

According to Yahoo! Sports, Anthony Johnson was suffering from a form of cancer known as non-Hodgkin’s lymphoma and hemophagocytic lymphohistiocytosis, an auto-immune disease. He died of organ failure after a long fight with these illnesses.

Both conditions involve out-of-control production of white blood cells, while hemophagocytic lymphohistiocytosis (HLH) is a rare condition where those cells build up in the spleen and liver, damaging the organs and interfering with multiple other functions in the body. HLH is typically seen in infants and children, but can also be caused by cancer.

According to Johnson’s close friend Kamaru Usman, Anthony didn’t like to share details of his illness.

“You know, it was a little like [Black Panther actor] Chadwick Boseman,” Usman told Yahoo! Sports. “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.”

The MMA community was sad to hear about the passing of “Rumble,” who built a reputation over his decade at the top of the sport as one of the most feared knockout artists around. After struggling with weight issues for years as a welterweight and middleweight, Johnson finally found his place in the UFC light heavyweight division where he challenged for the title twice, losing both times to Daniel Cormier.

“Rest Easy my brother,” Cormier wrote on Twitter. “For a guy who struck fear in so many peoples heart Anthony Johnson was a caring person. 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.”

Other fighters to pay tribute to “Rumble” online included former light heavyweight champion Glover Teixeira, who ended up on the bad end of a 13 second knockout, one of twelve first round knockouts on Johnson’s 23-win record.

“I am so sad to hear about this news,” Teixeira wrote. “One of the most scary and tough opponents that I had ever faced, and one of the nicest and most humble humans I have ever met. My heart is broken. My condolences to his family.”

I am so sad to hear about this news. One of the most scary & tough opponents that I had ever faced and one of the nicest and most humble humans I have ever met. My heart is broken. My condolences to his family. RIP #rumblesquad

— glover teixeira (@gloverteixeira) November 13, 2022

Teammates past and present also shared their thoughts and feelings on his passing.

Incredibly saddened by the news. Rumble, you were one of the coolest and most realest human I’ve ever met. You gave me so much invaluable advice throughout my career and I can’t believe you’re gone.

— Dan Ige (@Dynamitedan808) November 13, 2022

Rest in Peace Anthony Johnson

Descanse em paz Anthony Johnson

— Charles ‘DoBronxs’ Oliveira (@CharlesDoBronxs) November 13, 2022

Rip Rumble. Only met him once or twice, such a gentle giant, super sweet to me, the random new UFC fighter he had never heard of, biggest hand I ever shook. It’s a sad day to lose such a legend.

— Angela Hill (@AngieOverkill) November 13, 2022

Sometimes I feel like I work so much that I miss out on “living” with the ones I care about the most. I hope everyone out there is taking care of themselves as best as they can and making memories you’ll never forget.

— Aljamain Sterling (@funkmasterMMA) November 14, 2022

Crushed and devastated to learn that @Anthony_Rumble has passed away. AJ was one of the good guys, he was a great man with a huge heart. God Bless you AJ, I will miss you my brother. RIP Rumble

— Big John McCarthy (@JohnMcCarthyMMA) November 13, 2022

We’ll leave this post with one of the funnier moments from Anthony Johnson’s time in the UFC: when he and Jon Jones trolled Dana White with a fake press conference brawl. This was shortly after Jones and Daniel Cormier had gotten into a very real face off brawl, so White fell for the prank hook, line, and sinker.

Rest in peace, “Rumble.”