Who dated Kathleen Cavendish, Marchioness of Hartington?

Kathleen Agnes Cavendish, Marchioness of Hartington (née Kennedy; February 20, 1920 – May 13, 1948), also known as "Kick" Kennedy, was an American socialite. She was the second daughter of Joseph P. Kennedy Sr. and Rose Fitzgerald, a sister of U.S. President John F. Kennedy and Senators Robert F. Kennedy and Ted Kennedy, and the wife of the Marquess of Hartington, heir apparent to the 10th Duke of Devonshire.

When her father was serving as U.S. Ambassador to the United Kingdom, Kathleen made many friends in London and was the "debutante of 1938". Working with the Red Cross, she began a romantic relationship with Lord Hartington, whom she married in May 1944. He was killed on active service in Belgium only four months later. Kathleen died in a plane crash in 1948, flying to the south of France while on vacation with her new partner, the 8th Earl Fitzwilliam.

William Henry Lawrence Peter Wentworth-Fitzwilliam, 8th Earl Fitzwilliam, DSO (31 December 1910 – 13 May 1948), styled Viscount Milton before 1943, was a British soldier, nobleman, and peer, with a seat in the House of Lords.