High Quality Content by WIKIPEDIA articles! Catherine Seymour, Countess of Hertford (25 August 1540 – 26 January 1568), born Lady Catherine Grey, was the younger sister of Lady Jane Grey. A granddaughter of Henry VIII`s sister Mary, she was a potential successor to her cousin, Queen Elizabeth I of England, but incurred Elizabeth`s wrath by her secret marriage to Edward Seymour, 1st Earl of Hertford. Following her arrest when the queen was informed of her clandestine marriage, she lived in captivity until her death, having borne two sons in the Tower of London.