Duke of Montagu

The title of Duke of Montagu has been created several times. It was first created in the Peerage of England in 1705 for Ralph Montagu, 3rd Baron Montagu of Boughton, with the subsidiary title Marquess of Monthermer, but became extinct in 1749. The first Duke had been created Earl of Montagu and Viscount Monthermer in 1689. The Dukedom was then recreated in the Peerage of Great Britain in 1766 for the late Duke's son-in-law, George Montagu (né Brudenell), 4th Earl of Cardigan, with the subsidiary title Marquess of Monthermer. On his death in 1790 the dukedom and marquessate became extinct, and the earldom passed to his brother, James Brudenell, 5th Earl of Cardigan. The dukedom is named for the ancient Anglo-Norman family rather than any place.

...
Wikipedia