Lady Pemberton is based on Elizabeth Herbert, Countess of Pembroke
and Montgomery. She was the daughter of Elizabeth Trevor and Charles
Spencer, 3rd Duke of Marlborough. In 1760, the Countess of Pembroke
became the Lady of the Bedchamber to Queen Charlotte, a duty which
the fictional Lady Pemberton shares.
John "Gentleman" Jackson, the former heavyweight champion of
England and the teacher of the "Sweet Science" to the members of the
Ton, makes his appearance in Lord Wellesbourne, indirectly.
Wellesbourne is one of his students.
Henry Angelo had a Fencing Academy on Bond Street near John "Gentleman" Jackson's boxing club. He, too, makes an indirect appearance in the book as Wellesbourne frequents Angelo's fencing academy also.