Question: What American Socialite married the elder son of Edward Cavendish?
Sentence (from "Kathleen Cavendish, Marchioness of Hartington"): She was the daughter of Joseph P. Kennedy, Sr. and Rose Kennedy, sister of future U.S. President John F. Kennedy, and wife of the Marquess of Hartington, heir apparent to the 10th Duke of Devonshire.
Relevant evidence: No