Aristotle Onassis's health became worse after the death of his son Alexander in a plane crash in 1973. Aeristotle Onassis died of respiratory failure caused by myasthenia gravis at aged 69 in Paris on March 15, 1975. After two years of legal wrangling, Kennedy Onassis accepted a settlement of $26 million from Christina Onassis, Aristotle's daughter.