Famously protective of his private life, Prince was enigmatic even to those who worked with him, revealing little about his personal life and nothing about any ongoing health struggles prior to his death at his Paisley Park compound Thursday at 57.
"He was never a robust guy, let's be honest. He worked hard, and all the time, but if he was ill, he was so incredibly private, you would never be told it, you would never know it," an industry source tells PEOPLE of the megastar.
The Minneapolis native eschewed spotlight through the years, preferring his Paisley Park sanctuary in Chanhassen, Minnesota, to flashier environments in New York or Los Angeles.
"He was reclusive. That was Prince," says the source. "For him, doing anything beyond making music, in the public arena, that was like being stuck with needles. He hated it. His focus was purely on music, always."
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Prince's death comes after the iconic singer was battling the flu for several weeks. Last Friday, the Purple Rain singer's private plane made an emergency landing to rush him to a hospital in Moline, Illinois. He was released three hours later.
The source said the singer was not forthcoming about any health struggles – which was characteristic of the musician who savored his privacy.
"If he was ill or suffering, that's not something you would reasonably expect to know," said the source. "It's not surprising to me that [his death] was surprising."