William John Robert Cavendish, Marquess of Hartington and Kathleen Cavendish, Marchioness of Hartington

Kathleen Kennedy and William John Robert Cavendish, the Marquess of Hartington are shown on their wedding day, May 6, 1944. Kathleen Kennedy is the sister of President John F. Kennedy. Kennedy's brother, Joseph P. Kennedy, Jr. is pictured at right. Cavendish and Joseph P. Kennedy, Jr. were killed in World War II. Kathleen Kennedy died in a plane crash in 1948 at age 28. (Photo: AP Photo | Date: May. 17, 2012)