Mislabeled pills were seized at the home of musician Prince after his death from an overdose of the powerful opioid fentanyl, according to media reports on Monday.

Prince died on April 21 at his home and studio outside Minneapolis, and investigators are trying to establish how he ingested fentanyl, with one theory being that he may have accidentally taken the drug because it was not properly labeled.

Pills containing fentanyl were seized at his home, but they were marked hydrocodone, the Star Tribune said, citing an unnamed source. The source also told the newspaper that Prince did not possess a prescription for fentanyl.

Among medications found in a dressing room, and in suitcases and bags, was an Apleve bottle that contained pills stamped "Watson 385," which is used on hydrocodone-acetimonophen pills. But at least one of those pills contained fentanyl, the Associated Press reported, also citing an anonymous source with knowledge of the investigation.

A spokeswoman for the medical examiner's office that has investigated Prince's death did not confirm or deny the reports.

Fentanyl, which is often sold illegally and has caused an epidemic of overdose deaths around the United States, is the most potent narcotic known, 50 times stronger than heroin.

The megastar did not leave a will when he died unexpectedly at age 57. A flood of individuals have tried to make claims on his estate, which some have valued at more than $500 million. A judge excluded 29 would-be heirs in July, bolstering the claims of his sister and surviving half-siblings.