William Cavendish-Bentinck
Dorothy Bentinck, Duchess of Portland ("née" Lady Dorothy Cavendish; 27 August 1750 – 3 June 1794) was Duchess of Portland as wife of William Cavendish-Bentinck, 3rd Duke of Portland, the Prime Minister of Great Britain. She is also a great-great-great-grandmother of Queen Elizabeth II through the queen's maternal grandmother.