An official autopsy report released Thursday confirmed that Prince died of an accidental overdose of prescription painkillers.
The report by the Midwest Medical Examiners' office said that Prince died from an accidental overdose of fentanyl, a powerful prescription painkiller.
Prince administered the drug himself, the medical examiners' office said.
The release of the public autopsy report followed weeks of speculation about the pop superstar's rumoured struggles with painkiller addiction leading up to his death.
Prince, 57, was found dead by a longtime friend and his personal assistant in an elevator at his Paisley Park compound near Minneapolis on April 21.
The autopsy report said he was wearing a black shirt, pants and cap, with black underwear and socks and a grey undershirt.
According to news reports, Prince had been treated the day before for opioid withdrawal symptoms and had been scheduled to meet with a doctor specializing in opioid addiction the next day.
Fentanyl is a synthetic opioid painkiller used to treat severe pain. It is available in the US only by prescription, but is often abused by addicts and sold illegally.
It was unlear whether Prince had a prescription for fentanyl, the Minneapolis Star-Tribune reported.
Sources close to the investigation into Prince's death told the newspaper authorities were looking at how he obtained the drugs.