in 1980 he succeeded his elder brother ferdinand cavendish-bentinck as the 9th duke of portland. upon his own death in 1990, the dukedom and the marquessate of titchfield became extinct because his only son had predeceased him and there were no other surviving male heirs of the 1st duke. however, the earldom of portland had been created in an earlier generation than the dukedom and there were surviving descendants in the male line to inherit it. that title was therefore inherited by his kinsman, henry noel bentinck, who became 11th earl of portland, together with its subsidiary titles of viscount woodstock and baron cirencester. he was interred at the traditional burial place of the dukes of portland in the churchyard of st winifred's church at holbeck.