Prince reportedly worked for 154 hours straight without sleep in the days before he was found dead inside his Paisley Park estate.
Speaking after a private family service at the estate, the artist's brother-in-law Maurice Phillips reportedly claimed the singer worked for six days before his death.
Mr Phillips said: "He worked 154 hours straight. I was with him just last weekend. He was a good brother-in-law".
Meanwhile, the star's brother-in-law told The Sun his estate will be turned into a museum as a lasting memorial.
Mr Phillips told the newspaper: "It would be for the fans. He was all about the fans - this would remember his music, which is his legacy".
"Prince was always private but would have wanted his music remembered".
Prince was found collapsed in a lift at Paisley Park by staff members on Thursday.
He was last seen alive 12 hours earlier when he was dropped off at the estate. He was pronounced dead at the scene.
"No obvious signs of trauma"
Police are investigating the circumstances surrounding the death after authorities said they had "no reason to believe" Prince took his own life.
Authorities added that there were "no obvious signs of trauma" on his body.
Employees at the Electric Fetus record shop in Minneapolis said the musician appeared to be "pale" and "weak" when he visited five days before his death.
Max Timander, who works at Electric Fetus, told the Press Association: "Everyone I've talked to on that Saturday said he looked kind of pale and he was not totally looking in the best shape as he normally is".
"It sounded like he was looking kind of weak. I know he had just got over the flu supposedly".
A state Senator in Prince's home state of Minnesota has, meanwhile, called for it to adopt purple as its official colour, reported the St Paul Pioneer Press. Minnesota currently does not have an official colour.
Sales of Prince's music have skyrocketed worldwide since the artist's death last week and several songs or albums are expected to make it into the next UK chart when it is published on Thursday.
The mayor of Chanhassan, the city which is home to Paisley Park, said a private funeral service will be held for Prince in early May.
