William Cavendish, 4th Duke of Devonshire, styled Lord Cavendish before 1729, and Marquess of Hartington between 1729 and 1755, was a British Whig statesman and nobleman who was briefly nominal Prime Minister of Great Britain. He was the first son of William Cavendish, 3rd Duke of Devonshire and his wife, Catherine. He is also a great-great-great-great-great-grandfather of King Charles III through the king's maternal great-grandmother, Cecilia Bowes-Lyon, Countess of Strathmore and Kinghorne. Born: May 8, 1720 Died: October 2, 1764 In office: November 16, 1756 – June 25, 1757 Wiki link