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 Brudenell, 5th Earl of Cardigan.

The dukedom is named after the Montagu family "of Boughton" in Northamptonshire, where the 1st Duke built the splendid and surviving Boughton House, which claimed descent from the ancient Anglo-Norman family of Montagu, Earls of Salisbury, which connection is however unproven.

[3] It is suggested by the Complete Peerage[4] that the Ladde family adopted the surname of Montagu due to "having to deal with some Montagu inheritance", i.e. dictated by the terms of a bequest from a member of that family, as was common practice, requiring the legatee to adopt the surname and arms of the legator, where a branch of a family had died out in the male line.

The Montagu family of Boughton and its descendants use the coat of arms of Montagu, Earls of Salisbury, but differenced by a bordure sable, and quarters the arms of Monthermer, as did the Earls of Salisbury, but undifferenced.