Duke Hamilton had fought with Lord Mohun
Note by Heny Craik to Letters 55 from Journal To Stella

This was the duel introduced in Thackeray's Esmond. The death of the Duke was not, according to the most trustworthy accounts, due to such foul play as Swift imagines, but the profligate character of Lord Mohun and his associates lent credibility to the story. The quarrel arose out of some dispute as to an inheritance. The Duke of Hamilton was the leading Scotch nobleman, and was, by descent, wealth, and position, one of the chief of the Tory party.