FILE PHOTO - Musician Prince gestures on stage during Apollo Theatre's 75th anniversary gala in New York. Picture: Reuters

Nearly two years after music icon Prince was found unresponsive at his Paisley Park estate in Minnesota, a toxicology report of the star's autopsy obtained on Monday by The Associated Press, revealed that he had an "exceedingly high" concentration of fentanyl in his body when he died.

Public data released six weeks after his death on 21 April 2016, showed Prince died of an accidental overdose of fentanyl, a synthetic opioid 50 times more powerful than heroin.

The report says the concentration of fentanyl in Prince's blood was 67.8 micrograms per litre. 

The report also says the level of fentanyl in Prince's liver was 450 micrograms per kilogram, and notes that liver concentrations greater than 69 micrograms per kilogram "seem to represent overdose or fatal toxicity cases."

Read: 'Prince knew when he was going to die'

Dr. Charles McKay, president of the American College of Medical Toxicology, said generally speaking, the findings suggest Prince took the drug orally, while fentanyl in the blood and liver suggest it had some time to circulate before he died.

Search warrants released about a year after Prince's death showed authorities found numerous pills in various containers around his home.