 Her nephew William Cavendish, Marquess of Hartington, married Kathleen Kennedy, a sister of John F. Kennedy.In 1929 Lady Dorothy began a lifelong affair with the Conservative politician Robert Boothby, an arrangement that scandalised high society but remained unknown to the general public.Philip Frere, a partner in Frere Cholmely solicitors, urged Macmillan not to divorce his wife, which at that time would have been fatal to a public career even for the "innocent party".