A press release from the Midwest Medical Examiner's Office in Minnesota said that the singer died from an accidental fentanyl overdose, which he "self-administered."
Fentanyl is a powerful opiate, affecting the central nervous system. The drug is 30 to 50 times more powerful than heroin and 50 to 100 times as potent as morphine.
The iconic musician was found dead in his home in Paisley Park, Minnesota, on April 21. He was 57. An autopsy was completed a day later.
The release also stated that Prince had scars on his left hip and right lower leg.
Although the singer didn't have any known ailments, his former fiancée and music collaborator Sheila E. told "Good Morning America" the day after his death that he suffered many injuries from performing.
"We know that he's had issues with his hips," she said. "If you look back in the days of 'Purple Rain' when he was on top of risers and jumping down off risers in those heels, you know, it damaged parts of his body."
She added, "I know we're always injured when we play onstage. I don't know anything other than that."
Prince was an avid performer and was on his "Piano and a Microphone" tour days before he died.
"People use medication. The question is, are you on meds in a dangerous way?" he said, noting that Prince was a vegan.
"Everybody who knows Prince knows he wasn't walking around drugged up," McMillan said. "That's foolish. No one ever saw Prince and said, 'He looks high.' It wasn't what he was about."
But there were clues that Prince may have struggled with opioid use. The day before he died, his team contacted Dr. Howard Kornfeld, a California-based opioid-addiction specialist, according to attorney William Mauzy.
Mauzy said that Kornfeld's son Andrew Kornfeld was sent to meet with the singer but that after he arrived at Paisley Park, he, among others, discovered Prince unconscious in an elevator.
A search warrant connected to the death investigation showed Prince met with Dr. Michael Todd Schulemberg on April 7 and 20. Schulemberg, who was delivering the results of medical tests on April 21, was among those present when the singer's body was discovered.
Prince's sister Tyka Nelson said in a Facebook post that the family will hold an official memorial in August.