A Minnesota medical examiner says Prince died of an accidental fentanyl overdose.

Fentanyl is a powerful painkiller administered with a transdermal patch.

The report from the Midwest Medical Examiner's Office was issued Thursday, more than a month after the music superstar was found dead at age 57 at his Paisley Park mansion.

The single-page report said Prince "self-administered fentanyl," referring to a synthetic opioid many times more potent than heroin.

The report was signed by Quinn Strobl, the office's chief medical examiner.

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