In the weeks since the 57-year-old singer was found dead at his suburban Minneapolis compound, on 21 April, investigators have been looking into whether he had a prescription drug problem.

This surprised friends and family members, who said Prince avoided alcohol and drugs and maintained a healthy lifestyle.

On Thursday, however, medical examiner A Quinn Strobl released the office’s assessment of Prince’s cause of death: “self-administered fentanyl”, a powerful opioid. The office said it could not offer further comment.

In a press release, the Carver County sheriff’s office said it “continues its investigation”.

Earlier on Thursday Minneapolis Star Tribune reported that Prince died of a painkiller overdose.

The official autopsy and toxicology reports have yet to be released.

Prince was last seen alive around 8pm on 20 April, when he was dropped off by an acquaintance at Paisley Park, his sprawling compound in Chanhassen, Minneapolis, his longtime hometown. Two staff members appeared at the residence early on the following day, and discovered his body in an elevator on the first floor.

Law enforcement officials have said there were no “obvious signs” of trauma on Prince’s body, and there were no indications of foul play or suicide.

Prince’s team was organizing treatment with a California addiction doctor to help him kick an addiction to painkillers. According to a search warrant obtained by news agencies, the day before Prince’s death a local doctor treated him for fatigue and anemia, stemming from apparent opioid withdrawal.

The doctor, Michael Todd Schulenberg, treated Prince twice in April and prescribed him medication. The warrant did not specify the type of medication.

An attorney, William Mauzy, later told reporters Prince’s representatives contacted the California addiction doctor, Howard Kornfield, on 20 April. Kornfield, who could not immediately fly to Minnesota, sent his son, Andrew, to meet Prince the day the singer’s body was found.

According to a transcript of the 911 call, a caller stated he did not know the address of Paisley Park and, at first, mistakenly said it was located in Minneapolis. Mauzy confirmed that Andrew Kornfield made the 911 call.

The younger Kornfeld, who is not a doctor, was carrying buprenorphine, a medication that can be used to treat opioid addiction by easing cravings and withdrawal symptoms, Mauzy said, explaining that he intended to give the medication to a Minnesota doctor who had cleared his schedule to see Prince on 21 April.

Mauzy has refused to identify that doctor. Schulenberg is not authorized to prescribe buprenorphine.

Prince’s death followed a chaotic scene after his last shows, on 14 April in Atlanta. Following the shows, Prince boarded a private jet to return home. Just over an hour into the flight, the plane was abruptly diverted, descending 45,000ft in 17 minutes for an emergency landing.

A bodyguard carried an unconscious Prince from the plane, records show, and the singer was sent to a local hospital to be treated for a suspected overdose of painkillers.

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