What killed Evel?

Since it wasn't a spectacular motorcycle crash that killed Evel Knievel, what was it? I wanted to know too. Here's what I found:

"Knievel died in Clearwater, Florida on November 30, 2007, at the age of 69. He had been suffering from diabetes and pulmonary fibrosis for many years. Longtime friend Billy Rundel reported that Knievel had trouble breathing while at his residence in Clearwater, but died before the ambulance could reach the hospital. "It's been coming for years, but you just don't expect it. Superman just doesn't die, right?" was Rundel's reaction." says Wikipedia quoting a story from ESPN.