[citation needed] In 1767 he assumed by Royal licence the additional surname of Bruce.

In June 1776 he was created Earl of Ailesbury (later styled Aylesbury), in the County of Buckingham,[3] a revival of the earldom which had become extinct on his uncle's death.

[4][5] Lord Ailesbury married firstly, Susanna Hoare, daughter of the banker Henry Hoare and widow of Charles Boyle, Viscount Dungarvan, on 17 February 1761; her only child from her first marriage was Henrietta O'Neill, later a successful poet.

Lord Ailesbury died at Seamore Place, Mayfair, London, in April 1814, aged eighty-four.

He was succeeded in the earldom by his third but only surviving son, Charles, who was created Marquess of Ailesbury in 1821.