Desc: The Fatal Weakness: Directed by Norman Lloyd. With Gretchen Corbett, Dennis Dugan, John McMartin, Charlotte Moore. The Fatal Weakness was written by American Playwright George Kelley, who happened to be Grace Kelly's uncle. It concerns an upper class married woman whose fatal weakness is attending weddings of people even when she does not know them. She is an incurable romantic so when she suspects that her husband of many years is having an affair, she elicits the help of her best friend to find out the truth. This drawing room comedy has a lot to say about marriage, fidelity, and fatal weaknesses.