Official: Prince’s cause of death has now been confirmed.

Tests have shown that superstar musician Prince died of an opioid overdose.

A law enforcement official, who is close to the investigation, told AP this was established by tests after the singer’s death in April.

The 57-year-old singer was found dead on April 21 at his Minneapolis-area estate. The official, who is close to the investigation, spoke on condition of anonymity because he was not authorised to speak to the media.

A single page report is said to have stated that Prince “self-administered fentanyl” – a synthetic opioid many times more potent than heroin.

Tests have shown that superstar musician Prince died of an opioid overdose. Via Getty.

The findings confirm suspicions that opioids played a role in the musician's death.

The Star Tribune in Minnesota also quotes a separate source with knowledge of Prince's death investigation who says he died from an overdose of painkillers.

Prince's death came less than a week after his plane made an emergency stop in Moline, Illinois, for medical treatment as he was returning from a concert. The official said Prince was found unconscious on the plane and that first responders gave him a shot of Narcan, an antidote used in suspected opioid overdoses.

It was reported shortly after Prince's death that the highly addictive painkiller Percocet - which contains both acetaminophen and oxycodone - had been found in his system.

Prince was pronounced dead at 10:07 a.m. on April 21.

Investigators said he was last seen alive at about 8 p.m. the night before at Paisley Park.

Prince’s estate manager and personal assistant discovered the singer’s lifeless body in a Paisley Park elevator at about 9:40 a.m. Andrew Kornfeld, the son of a well-known addiction and pain management doctor, phoned 911 after arriving at the estate.

Prince during the Super Bowl 2007 in Miami, Florida. Via Getty.

An autopsy revealed no signs of trauma, and Carver County Sheriff Jim Olson has said previously that investigators don’t believe Prince committed suicide.

It has been reported Prince may have started abusing medications following hip surgery several years ago.

Detectives have already questioned a doctor who saw the 57-year-old twice in the weeks before he died.

Prince’s funeral will be held in August. Via Getty.

A police warrant has also revealed that Dr Michael Schulenberg prescribed medication to the singer on 20 April - the day before he died.

It was also revealed that Prince was expected to meet with an addiction specialist the day of his death after his representatives called California's Recovery Without Walls outpatient clinic to say he was "dealing with a grave medical emergency." Dr. Howard Kornfeld's attorney said during press conference that he and his son, who called 911 on Prince's death but was not a doctor,  planned to advise Prince on treatment for a prescription drug addiction.

Prince’s funeral will be held in August.