Katharine Margaret Alice Macmillan, Viscountess Macmillan of Ovenden DBE (née Ormsby-Gore; 4 January 1921 – 22 January 2017) was the daughter of the 4th Baron Harlech, granddaughter of the 4th Marquess of Salisbury and great-granddaughter of the 10th Marquess of Huntly. On 22 August 1942, she married Conservative politician Maurice Macmillan, making her the daughter-in-law of fellow Conservative politician Harold Macmillan, who would serve as prime minister from 1957 to 1963. They had five children together: She died on 22 January 2017.