Prince reportedly had a history of using the prescription painkiller Percocet.

A source said the pop star's eye-catching performance style took a toll on his body towards the end of his life, and proof of this was that he was often seen out walking with a cane.

An autopsy was conducted on Prince's body in the hours after his death at Paisley Park, his estate just outside Minneapolis.

And although the medical examiner said there were "no obvious signs of trauma," the toxicology reports may take weeks to complete.

Meanwhile, another source told People magazine that the legendary singer had been struggling with an "ongoing illness" at the time of his passing, which came a week after his private plane was forced to make an emergency landing in Moline, Illinois so that he could attend a nearby hospital.

An insider said: "The people close to him were very concerned for his health and indicated he'd been undergoing treatments which made his immune system weak."