(Photo by Al Powers/Zuffa LLC/Zuffa LLC via Getty Images)

Four months after his unexpected death, officials have revealed a cause behind the tragic passing of UFC Hall of Famer Stephan Bonnar. He died in December at the age of 45.

Per MMA Fighting, the Clark County Coroner’s Office in Las Vegas revealed that Bonnar died from an accidental fentanyl overdose. The report indicates that the UFC star passed away on Dec. 22 from “fentanyl, parafluorofentanyl and mitragynine intoxication.”

In an Instagram post in December, UFC revealed the sad news about Bonnar’s passing.

“The UFC family is saddened by the passing of UFC Hall of Famer Stephan Bonnar. We send our sincerest condolences to his family and friends.”

At the time of his death, UFC said Bonnar died because of “presumed heart complications.”

UFC president Dana White also released a statement on Bonnar’s death in December.

“Stephan Bonnar was one of the most important fighters to ever compete in the Octagon,” Dana White said. “His fight with Forrest Griffin changed the sport forever, and he will never be forgotten. The fans loved him, related to him and he always gave them his best. He will be missed.”

Bonnar retired from UFC with a 17-9 record. He was inducted into the Hall of Fame in 2013.

Stephan Bonnar entered UFC during first season of The Ultimate Fighter

Bonnar joined UFC during the first season of The Ultimate Fighter in 2005. He was part of one of the greatest fights of all-time against Forrest Griffin.

While speaking about the fight, Bonnar said, “I knew it was a good fight during the fight. It hit me when everyone started stomping their feet and it felt like the whole place was shaking. And that was in the second round. I was like, ‘ooooh, this must be good.’” 

Bonnar discussed how the show and the sport changed his life.

“I didn’t think I’d have a UFC career,” he said. “It was just a little hobby I was doing, so it changed everything. Almost overnight, I became like a celebrity. Everywhere I went, someone would recognize me, even in obscure places.

“I was traveling with Tapout, and we were in a small town. I was jogging and someone in a pickup was going ‘Hey Bonnar.’ And everywhere you go, someone knows who you are. It was wild.”

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