With no child of her own to take the throne after she died, Mary was forced to accept that her younger half-sister Elizabeth was the next rightful heir. Mary had always had health problems especially concerning her reproductive organs and in 1558 she died at the age of 42 possibly from ovarian cysts or uterine cancer. When she died, Philip wrote a letter to his sister Joan stating "I felt a reasonable regret for her death". Her will specifically expressed her desire to be buried next to her mother, but instead she was interred in Westminster Abbey. Years later, when Mary's sister Elizabeth died, she was buried in Mary's grave on top her long dead sister. Elizabeth's presence in the grave is greatly celebrated by a magnificent monument. The fact that Mary is also interred there is acknowledged only by the monument's inscription "Partners both in throne and grave. Here rest we two sisters Mary and Elizabeth in the hope of one resurrection".