William Cavendish-Bentinck
Bentinck was the second son of William Bentinck, 2nd Duke of Portland, by Lady Margaret Cavendish Harley, daughter of Edward Harley, 2nd Earl of Oxford. He was the only brother of Prime Minister William Cavendish-Bentinck, 3rd Duke of Portland. He was educated at Westminster and Christ Church, Oxford, and went on a Grand Tour between 1764 and 1766.