Kathleen Agnes Cavendish, Marchioness of Hartington ( 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 Kennedy as well as a sister of U.S. President John F. Kennedy and Senators Robert F. Kennedy and Edward M. "Ted" Kennedy and the wife of the Marquess of Hartington, heir apparent to the 10th Duke of Devonshire. When her father was serving as United States 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. Early years Kathleen Agnes Kennedy was born at home at 83 Beals Street in Brookline, Massachusetts on February 20, 1920, the fourth child and second daughter of Joseph P. Kennedy Sr. and Rose Fitzgerald. She was nicknamed "Kick" because of her "irrepressible nature". Kathleen was especially close to her older brother, John F. Kennedy, known as "Jack". Her other siblings were Joseph Jr., Rosemary, Eunice, Patricia, Robert, Jean and Ted. Kathleen was educated at Riverdale Country School in the Riverdale section of the Bronx, New York City. She also attended Noroton Convent of the Sacred Heart in Noroton, Connecticut, and the Holy Child Convent in Neuilly, France. While the Kennedy daughters were not raised to have political ambitions like their brothers, they were nonetheless provided with many of the same educational and social opportunities, owing to their father's powerful financial and political connections and influence. This was particularly the case when President Franklin D. Roosevelt appointed Joseph as United States Ambassador to the United Kingdom in 1938. As a child, Kathleen was very athletic and played football with her brothers. Her optimism and high spirits attracted many suitors, some of whom were Jack's closest friends. When Kathleen attended the Riverdale Country School, her mother did not approve of the male attention she attracted, and sent her to the all-girls Noroton Convent of the Sacred Heart. Eventually, Kathleen started to date, and had her first serious relationship with, Peter Grace, an heir to W. R. Grace