By ALICE PARK Alice Park – Sat Jun 27, 7:10 am ET

Late Thursday afternoon, after nearly two hours of speculation, the Los Angeles coroner confirmed that Michael Jackson had died, apparently of cardiac arrest. Hundreds of fans gathered around UCLA Medical Center, where the 50-year-old "King of Pop" had been rushed reportedly after collapsing at home.

Jackson's sudden death raised immediate questions about the singer's health history. But little is known about his medical record, which has always been a mystery, characterized largely by rumors and speculation - which sometimes seemed just the way he wanted it. In the fishbowl world he inhabited - with his three young children, Michael Joseph Jackson Jr. (a.k.a. Prince Michael), Paris Michael Katherine Jackson and Prince Michael Jackson II - Jackson has managed to spark, then dodge, questions surrounding his various health problems. Much of time, the superstar behind such hits as "Beat It," "Thriller" and "Billie Jean" appeared to invite speculation, appearing in public wearing a surgical mask, as he did a decade ago, or in a wheelchair, which he used on certain occasions last year. The singer was always very thin and appeared frail. (See the top 10 Michael Jackson moments.)

The health questions began early in his solo career, mostly surrounding his apparent plastic surgery, and continued as photographs documented his oddly lightening skin color. Jackson addressed that issue, acknowledging that he suffered from vitiligo, a skin disorder in which the pigment cells in the skin are destroyed, leaving white patches.

In 1984, the singer was hospitalized after receiving second-degree burns when his hair accidentally caught fire during the filming of a Pepsi commercial. Jackson reportedly used a hyperbaric oxygen chamber while he recovered and allegedly also slept in the chamber in an effort to halt the aging process - photos of him lying in one were leaked in 1986 - a claim he denied.

Around Christmas of last year, a British journalist working on a biography of the pop star revealed that Jackson was suffering from alpha-1 antitrypsin deficiency, a genetic condition that affects the lungs and liver. The author, Ian Halperin, told In Touch magazine at the time that Jackson needed a lung transplant and was bleeding in the intestines. He also claimed that Jackson couldn't see out of his left eye and was so winded that he could barely speak most of the time. Jackson's spokesman, Dr. Tohme Tohme, was widely quoted as denying the health problems, saying that the rumors were a "total fabrication" and that Jackson was "in fine health."

Recently, Jackson was preparing for a comeback tour, and when plans for a series of London shows were postponed in May, rumors emerged again that Jackson was sick - this time with skin cancer. Concert promoter AEG Live repeatedly declared in the press that the change in schedule had "absolutely nothing to do with Jackson's health."

It is unclear whether Jackson's sudden cardiac death has any relation to past conditions, but an autopsy is expected to occur on Friday.