While living in England, she was educated in London at Queen's College and quickly cultivated a wide circle of friends, both male and female, in British high society.

Following the German invasion of Poland and the outbreak of World War II in September 1939, Kick, who was staying at the family home in the south of France, had to rush to England with her friend Janey Kenyon Slaney.

Kathleen, having become very fond of England and the many friends she had made during her two years there, petitioned her parents to remain in London in spite of the coming danger.

In 1941, she decided to leave school, and began working as a research assistant for Frank Waldrop, the executive editor for the Washington Times-Herald.

[8][9] Kathleen's eldest brother Joseph P. Kennedy Jr., an officer in the United States Navy, to whom she had grown close during the last year of his life, as he was serving in Britain, was the only member of the family to attend the ceremony.

Popular on the London social circuit and admired by many for her high spirits and wit, Lady Hartington eventually became romantically involved with the 8th Earl Fitzwilliam,[10] who was in the process of divorcing his wife.

Once again, Rose Kennedy expressed her disapproval of her daughter's suitor and warned Kathleen that she would be disowned and cut off financially if she married Lord Fitzwilliam.

In an effort to gain his consent for her upcoming plans to marry Fitzwilliam, she decided to fly to Paris to meet with her father.

[11] On May 13, 1948, Lady Hartington and Lord Fitzwilliam were flying from Paris to the French Riviera for a vacation[12] aboard a de Havilland DH.104 Dove.

Approximately one hour into the flight, radio contact was lost with the plane when it entered the region near Vienne,[clarification needed] which was also close to the center of a storm.

The stress of the turbulence, coupled with the sudden change of direction, tore loose one of the wings, followed by both engines, and finally the tail.

The plane's fuselage then spun into the ground seconds later, coming to rest nose-down in a ravine, after striking terrain at Plateau du Coiron, near Saint-Bauzile, Ardèche, France.

She was buried on the Cavendish family burial grounds at St Peter's Churchyard, Edensor outside of Chatsworth, Derbyshire, England.