I can tell you right now what it was.
Prince had HIV from the late 90's and was being treated successfully. He converted to being a Jehoveh's Witness through a music pal. He stopped his medication 2 years ago because he was convinced by others God had cured him. When he stopped taking the medication cocktails, HIV eventually turned into full blown AIDS and once you stop that cocktail, the virus morphs and you cannot take it again and be successful at treating it as it is now immune to all those combinations once it mutates (Part of the drug cocktail is a process in which it kills the virus replication off and cannot react quick enough to the cocktail changes inherent in the treatment). Now, he is a goner.
He should have maintained his treatment.
Prince died of AIDS complications.