Please answer a question about the following article about Arnold Schwarzenegger:

On May 20, 1971, his brother, Meinhard, died in a car accident. Meinhard had been drinking and was killed instantly. Schwarzenegger did not attend his funeral. Meinhard was due to marry Erika Knapp, and the couple had a three-year-old son, Patrick. Schwarzenegger would pay for Patrick's education and help him to emigrate to the United States. Gustav died the following year from a stroke. In Pumping Iron, Schwarzenegger claimed that he did not attend his father's funeral because he was training for a bodybuilding contest. Later, he and the film's producer said this story was taken from another bodybuilder for the purpose of showing the extremes that some would go to for their sport and to make Schwarzenegger's image more cold and machine-like in order to fan controversy for the film. Barbara Baker, his first serious girlfriend, has said he informed her of his father's death without emotion and that he never spoke of his brother. Over time, he has given at least three versions of why he was absent from his father's funeral.

What caused Schwarzenegger's father Gustav's death?
stroke