In a letter sent from Downing Street at 9pm on the night of Pitt's duel with George Tierney (27th May 1798), Pitt writes to Dundas:
"Dear Dundas, You will perhaps hear that I had occasion to visit your neighbourhood this morning, in order to meet Mr. Tierney, in consequence of what passed between us in the House on Friday. We exchanged two shots on each side; and by the interposition of the seconds the affair ended in a way with which, I think, neither party had any reason to be dissatisfied. I am going to [Charles] Long's this evening, and will dine with you to-morrow. Yours ever, W. Pitt."
What an amusing way to make light of a duel! The duel was fought on a Sunday, which sparked some degree of outrage at the time, and also on the day before Pitt's 39th birthday. Fortunately, neither of the duellists were injured in any physical way, although Pitt was ill soon afterward.
Stanhope. (1862) Life of Pitt, Vol. 3. London: John Murray, p. 131.