Singer Prince, 57, who was found dead in his home in a Minneapolis suburb in late April, died of an accidental, self-administered overdose of an opioid painkiller, according to the county medical examiner death report on Thursday.

The Midwest Medical Examiner’s Office in Anoka County, Minnesota, had been investigating his death since he was found in an elevator in his home and studio on April 21.

“The decedent self-administered fentanyl,” the medical examiner’s report said, listing cause of death as “fentanyl toxicity” and noting it was accidental.

After prescription opioid medication was found at the scene, the investigation of Prince’s death had focused on painkillers, especially with reports stating that he had been struggling with an addiction and been scheduled to meet with a doctor who specializes in treating dependency.

Fentanyl is a highly addictive opiate that is more powerful than morphine and is used to treat patients with severe pain.

Prince, whose full name was Prince Rogers Nelson, did not leave a will, and his multimillion-dollar estate including royalties from his more than 30 albums is being handled by a court. The songwriter’s hits included “Purple Rain” and “When Doves Cry.”