Answer
The Duke of Portland is a title in the Peerage of England. The title was created in 1689 for William Bentinck, 1st Earl of Portland, who served as Lord Chamberlain of the Household to King William III and Queen Mary II. The Dukedom was created with a special remainder to the descendants of Bentinck's sister, Lady Anne Bentinck, who married Charles Fitzroy, 2nd Duke of Grafton.