[2] His paternal grandparents were Dacre Barrett and the former Lady Jane Chichester (eldest daughter of the 2nd Earl of Donegall).

His maternal grandparents were Thomas Lennard, 1st Earl of Sussex and Lady Anne Fitzroy (the illegitimate daughter of King Charles II and Barbara Villiers, Duchess of Cleveland).

[2] His mother had become suo jure Baroness Dacre in 1741 after the death of her elder sister, Lady Barbara Skelton (née Lennard), when the abeyance of her father's barony was terminated in her favor.

After visiting Naples, Florence, Venice and other Italian cities, the couple arrived in Rome around 1750, where they met painter Pompeo Batoni.

Anna was the daughter of Elizabeth Wilson and Sir John Pratt, an MP for Midhurst who served as Lord Chief Justice of England between 1712 and 1725.