A curious excerpt from The Pursuit of the Heiress, a history of aristocratic marriage in Ireland by A.P.W. Malcolmson, 2006:
Another strange tale, which this time ended less happily for the heir presumptive, is that of the 3rd Earl of Darnley, an eccentric bachelor who suffered from the delusion that he was a teapot. In 1766, when he was nearly fifty and had held the family title and estates for almost twenty years, Lord Darnley suddenly and unexpectedly married; and between 1766 and his death in 1781, he fathered at least seven children, in spite of his initial alarm that his spout would come off in the night.
I thought this couldn't possibly be true, but Malcolmson gives two sources, a letter from the Rev. George Chinnery to Viscountess Midleton, Aug. 18, 1762, kept at the Surrey History Centre in Woking, and a typescript family history by Rear Admiral W.G.S. Tighe. An Irish auction house supports the story.