A half-third cousin twice-removed of Princess Eugenie through Thomas Coke, 2nd Earl of Leicester, Brooksbank's great-grandfather was Sir John (Jack) Spencer Coke, a Gentleman Usher to King George VI and Extra Gentleman Usher to Queen Elizabeth II and his great-uncle was the 3rd Baron Hamilton of Dalzell. His parents are Old Etonian George Brooksbank, a company director and chartered accountant, and his wife, Nicola, who reside in London and Bordeaux in France. Jack has a younger brother, Thomas, who is also an Old Etonian.