2835544 William Henry Cavendish-Bentinck, 3rd Duke of Portland, 1792 (oil on canvas) by Lawrence, Thomas (1769-1830); Bristol Museum and Art Gallery, UK; (add.info.: William Henry Cavendish Cavendish-Bentinck, 3rd Duke of Portland KG PC (14 April 1738 ??30 October 1809) was a British Whig and Tory statesman, Chancellor of the University of Oxford, Prime Minister of Great Britain, serving in 1783 and Prime Minister of the United Kingdom from 1807 to 1809. The 24 years between his two terms as Prime Minister is the longest gap between terms of office of any Prime Minister. He was known before 1762 by the courtesy title Marquess of Titchfield. ); 穢 Bristol Museums, Galleries & Archives .