Mary's father encouraged Mary to adhere to liberal political theories and one of his followers, Percy Shelley, became Mary's lover while he was still married. He left his pregnant wife to be with sixteen-year-old Mary.
Mary broke the rules. She ran off with Shelley, had his babies prior to being married, marrying Percy Shelley after the death of his wife. Shelley drowned when he was only twenty-nine years old. After that Mary devoted herself to writing and to the raising of their only surviving child.
Mary Shelley died at the age of 53 of a brain tumor.