What caused the death of Eugen Sandow?

My boyfriend is a 260 lbs. bodybuilder and powerlifter. He just bought a book titled "Sandow the Magnificent" by David Chapman, and he has discussed it with me and our friends. Frederich Muller was born 2 April 1867 in Prussia. He became a professional strongman in stage shows and toured the world. He eventually wrote books about his training system, published a magazine about it and ran a chain of gyms in England. His stage name was Eugen Sandow. His mother was Russian, and he used her surname that was Sandov and became Sandow in the German spelling. He died 14 October 1925 at age 58.5 years. There seems to be several stories about what caused his death. Has anyone heard more about this? A curious fact in the matter is that Sandow's widow Blanche and two daughters refused to put a marker on his grave and didn't allow anyone else to do it either. That seems to indicate they had strong hostility toward him for some reason.