The title of Duke of Montagu has been created twice, firstly for the Montagu family of Boughton, Northamptonshire, and secondly for the Brudenell family, Earls of Cardigan. 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 1st 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 (together with the subsidiary title Marquess of Monthermer) for the late Duke's son-in-law George Brudenell, 4th Earl of Cardigan, who adopted the surname of Montagu. On his death in 1790 the dukedom and marquessate became extinct a second time, but the earldom passed to his brother, James Bru