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Prince stayed awake for “154 hours straight” despite being hooked on sleep-inducing painkillers , detectives have been told.

As the star ’s family gathered at his home for a memorial 24 hours after his private cremation, his brother-in-law told how the singer had not slept for six and a half days before he was found dead in a lift.

Maurice Phillips, who is married to Tyka Nelson, the Purple Rain star’s sister and only full blood relative, said: “I was with him just last weekend.

"He worked 154 hours straight. He was a good brother-in-law.”

Friends fear he may have been overprescribed drugs by a dodgy doctor.

(Image: Getty Images)

But Prince’s insomnia appears to clash with reports that he was taking high levels of painkiller Percocet, which is believed to have led to him overdosing aboard his private jet, five days before he died.

Read more:Prince fans at memorial service at Paisley Park given purple boxes full of memorabilia by his family

But, in extreme cases, users of the prescription drug have said it has kept them awake, especially when mixed with other medication.

(Image: FilmMagic)

Prince, 57, was found dead at his home at Paisley Park in Chanhassen, Minnesota, on Thursday.

Read more:Prince's ashes carried to waiting car under jacket after secret cremation

Detectives are understood to have discovered a number of prescription drugs there.

(Image: Splash News)

Authorities have said his death is not attributable to suicide or obvious trauma.

“Prince’s medical history is at the top of detectives’ list when it comes to cause of his death,” a police source said.

(Image: Splash)

Detectives want to find how the star obtained prescription-only drugs and whether they had been authorised by a physician.

Police have refused to comment on this but friends fear he may have been under the care of a “Dr Conrad Murray” medic, blamed for Michael Jackson’s death.

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He was found guilty of involuntary manslaughter in the 2009 death for administering a lethal dose of an anaesthetic.

Prince is reported to have been given a “save shot” used in overdoses after his pilot landed in Moline, Illinois.

(Image: FilmMagic)

Doctors advised he would need to be monitored for 24 hours but Prince left hospital and continued on his journey home from a gig in Atlanta.

On Saturday a man claiming to be Prince’s former drug dealer alleged the star was hooked on powerful opiates for over 25 years to overcome his stage fright.

(Image: Getty Images)

Using the name Doctor D, he said between 1984 and 2008, the singer spent up to £28,000 a time on six months supplies of Fentanyl patches and Dilaudid pills.

Both are highly addictive opioids.

Friends including Larry Graham and ex girlfriend Shiela E joined fans for the memorial at Paisley Park, where they were greeted by a sea of purple balloons.

Sir Elton John paid his respects in front of a sold-out Caesars Palace crowd in Las Vegas on Saturday.

And a jet made a vapour trail image of Prince’s icon in the sky at a New Orleans festival.