Hall of Fame fighter Stephan Bonnar, who played a significant role in the development and growth of UFC, died in December at the age of 45.
More than four months after his unexpected death, officials have released a cause of death.
The UFC announced shortly after his death in late December that Bonnar had died from “presumed heart complications while at work.”
But the Clark County coroner’s office in Las Vegas confirmed to MMA Fighting on Tuesday that Bonnar died from an accidental fentanyl overdose.
According to the report, Bonnar died from “fentanyl, parafluorofentanyl and mitragynine intoxication” on Dec. 22.
“Stephan Bonnar was one of the most important fighters to ever compete in the Octagon,” UFC president Dana White said in a statement at the time. “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.”
Largely considered one of the pioneers of UFC, Bonnar was inducted into the sport’s Hall of Fame in 2013.
He fought to a 17-9 record and had battles with UFC legends Jon “Bones” Jones, Anderson Silva and Tito Ortiz — the latter two fighters were his final opponents.
According to MMA Fighting, Bonnar opened up about his use of opioids in a 2021 interview with the outlet in which he claimed he was properly using them to treat long-term injuries suffered as a result of his career.
Fox News’ Ryan Morik and The Associated Press contributed to this report.