It happened Monday afternoon, but the university did not immediately release any further details.
Stewart resigned last summer and was replaced by Dana Holgorsen the same night.
Stewart had signed a six-year contract in September 2008. That agreement was amended in 2010 when Athletic Director Oliver Luck decided to replace him. He was as an assistant with the Mountaineers from 2000 to 2007.
Stewart also coached at Virginia Military Institute in Lexington from 1994 to 1996. He won eight games in three seasons as the Keydets coach. After VMI, Stewart went to the Canadian Football League, before resurfacing at West Virginia in 2000.
When Rich Rodriguez left for the head job at Michigan, Stewart was promoted to interim head coach and led the Mountaineers to a resounding 48-28 win over Oklahoma in the 2008 Fiesta Bowl. He was named the head coach at WVU the next day and led the Mountaineers to three straight 9-3 seasons before resigning in 2011. Virginia Tech wide receivers coach Kevin Sherman worked on Stewart's staff at VMI.
Sherman was on the road recruiting Monday, but he took time to reflect on the loss over the phone.
“He was a good man, good person, very passionate about the game of football,” Sherman said. “When he was at VMI, he was one of the coaches that really wanted to be there and be successful there. He was fair, honest, and tough. I'm just at a loss for words right now, but he's gonna be dearly missed.”
Here is a statement from VMI Athletic Director Donny White about Stewart's death:
"The VMI community is saddened to hear of the passing of Coach Stewart. He was respected and admired by many when he was here as our head coach for three seasons and he brought passion and energy to our football program with his enthusiasm for the Institute. He will be missed. Our hearts and prayers go out to his wife Karen and son Blaine."