Slayer Guitarist Cause of Death -- Band Says Rocker Died from Alcohol-Related Liver Failure

Slayer guitarist Jeff Hanneman died of alcohol-related cirrhosis -- scarring of the liver from years of heavy drinking ... this according to the band's official website.

The band posted a statement on its website ... saying, "While he had his health struggles over the years, including the recent Necrotizing fasciitis infection (AKA flesh-eating disease) that devastated his well-being, Jeff and those close to him were not aware of the true extent of his liver condition until the last days of his life."

"Contrary to some reports, Jeff was not on a transplant list at the time of his passing, or at any time prior to that. In fact, by all accounts, it appeared that he had been improving – he was excited and looking forward to working on a new record."

FYI -- Hanneman had several operations last year to remove dead tissue from his arm ... he believed he contracted the freaky, flesh-eating bacteria from a spider bite he suffered in a friend's hot tub.

Hanneman was the heart and soul of Slayer ... not only was he a HUGE guitar hero, but he also wrote several of their best-known songs, including "Raining Blood" and "Seasons in the Abyss."