In the morning of 26 May 1789, Prince Frederick Duke of York, engaged in a duel with Lieutenant Colonel Charles Lennox (later the 4th Duke of Richmond) who was a senior officer in the Coldstream Guards. The duel took place on Wimbledon Common and involved the use of pistols, although neither man was harmed.  While longstanding political and familial tensions existed between the Prince and Lennox, the immediate cause of the duel was unusual; apparently the Duke of York alleged that Lennox had been insulted during a function at a Daubigny's Club and according to the Duke Lennox had failed to address these offensive remarks appropriately. Charles Lennox insisted that he was unaware of any such statements and requested the Duke specify both what had been said and who had made the remarks. However, the Prince merely mentioned that the comments were uttered in his presence during a masked ball at Daubigny's Club, refusing to reveal either the content or the identity of the speaker. Lennox then wrote a letter to the members of club present at the function:

"Desiring each of them to let him (Lennox) know if he (the club member) can recollect any expression to have been used in his presence, which could bear the construction put upon it by his Royal Highness, and in such case, by whom the expression was used".

This was sensible investigation by Lieutenant Colonel Lennox, but it proved ineffective, turning up no further clarification of the matter and leaving Lennox no other option than to challenge the Duke of York again, and to eventually demand satisfaction for suggesting that he (Lennox) was too cowardly to respond to an alleged insult. These constructed circumstances appear to have been a ruse on the part of the Duke of York, who was probably trying to goad Lennox into a duel.

The Duke of York and Lennox had maintained a strained relationship before the incident at Daubigny's, despite Lennox serving in Prince Frederick's regiment, the Coldstream Guards, which he had joined at the expressed request of both the King and Prime Minister William Pitt; the Lennox family were favourites of King George III. So, Lennox's transfer would have probably caused some insult to the Duke of York who did not approve the transfer to his regiment. As a member of the Tory party, Lennox belonged to a faction that openly expressed dissatisfaction with the treatment of King George III, by his sons the Prince of Wales and the Duke of York, during periods when the King experienced episodes of mental illness (especially during the Regency). Given Lennox's Tory background and his uncle's association with the Pitt ministry, he would likely have joined in the public condemnation of the Prince of Wales and his Regency, which naturally extended to criticism of the Duke of York. For the Duke, any negative remarks about him and his brother, especially if made by a member of his regiment, would come across as both cowardly and ungrateful; reason enough for a confrontation. While the disagreement had some personal tension, its roots were also political.

On the day the duellists stood twelve paces apart and when cleared to do so Lennox was permitted to fire first and his pistol ball grazed the Prince's side curls. The Duke of York declined to fire his pistol and according to his second it was his intention not to fire his weapon. James Gilray portrayed the duel as an imaginary pugilistic encounter, with both men stripped to the waist with their seconds (see attached illustration with the Prince on the left and Lennox on the right). Obviously, there was some political sensitivities about portraying a duel with pistols, so boxing was substituted. As a footnote to the affair the officers of the Coldstream Guards held a "military convention" in the orderly room. They discussed the duel for two days, then they announced their judgment:

"It is the opinion of the regiment that Lieutenant Colonel Charles Lennox has behaved with courage; but, from the peculiarity of the circumstances, not with judgment".