On his nephew's death on 8 July 1779, he succeeded him as 5th and last Duke of Ancaster and Kesteven and Marquess of Lindsey and as 8th Earl of Lindsey.
Upon the demise of his nephew on July 8, 1779, he became the 5th and final Duke of Ancaster and Kesteven, and also the 8th Earl of Lindsey.