Kathleen Agnes, Cavendish, Marchioness of Hartington,(nee Kennedy;February 20,1920-May 13, 194 also known as "Kick" Kennedy. Was an American socialite. She was the daughter of Ambassador Joseph P. Kennedy and Rose Kennedy,sister of future U.S.President John F. Kennedy, and wife of William Cavendish, Marquess of Hartington, heir apparent to the Duke of Devonshire.