Premise: Larry Martin Hagman (September 21, 1931 November 23, 2012) was an American film and television actor, director and producer best known for playing ruthless oil baron J.R. Ewing in the 1980s primetime television soap opera "Dallas" and befuddled astronaut Major Anthony "Tony" Nelson in the 1960s sitcom, "I Dream of Jeannie".
Hypothesis: Larry Martin Hagman suffered a massive heart attack during one of his TV show appearances.