Counterfeit pills containing the synthetic opioid fentanyl were found at Princes estate in Minneapolis, the Associated Press reported Sunday.

A source associated with the investigation told the AP that inspectors found pills in an Aleve bottle that were falsely labeled as Watson 385, a common marking for pills that contain acetaminophen and hydrocodone. However, the AP reports that at least one of the pills tested positive for fentanyl, which is thought to be about 100 times stronger than morphine.

The 57-year-old artist died in April from what medical examiners determined was an overdose of fentanyl . The Minneapolis Star Tribune reports that the singer did not have a prescription for fentanyl at the time of his death. It appeared that Prince mightve consumed the counterfeit drugs without knowing that the pills contained fentanyl.

According to a report from the Drug Enforcement Administration issued in July, a large number of counterfeit prescription drugs containing fentanyl (or fentanyl-related compounds) are present in the U.S. drug market. Consumers of these counterfeit pills may be inadvertently ingesting fentanyl, as the drugs can only be detected upon laboratory analysis.

The Washington Post reports that authorities believe the illegally manufactured fentanyl is being produced in China and sold to drug traffickers in North America.

The Huffington Post has reached out to a representative for Prince and the Carver County Sheriff Office and will update this post accordingly.