Pop star Prince probably had no idea he was taking the deadly drug fentanyl and those closest to him didn't know he was in possession of it either, a Minnesota prosecutor has revealed.

Carver County Attorney Mark Metz announced on Thursday that no criminal charges will be filed in Prince's opioid overdose death in 2016.

Prince, 57, was found dead at his Paisley Park home and recording studio complex near Minneapolis on April 21, 2016. The official cause of death was a self-administered overdose of the painkiller fentanyl, which is 50 times stronger than heroin.

Metz said that musician died after taking a countefeit Vicodin painkiller than was laced with fentanyl.

"Prince had no idea he was taking a... pill that could kill him," Metz said.