Henry Petty-Fitzmaurice
On 21 April 1917, Lady Mary was married to Edward Cavendish, Marquess of Hartington. Edward was the eldest son of Victor Cavendish, 9th Duke of Devonshire and his wife, Evelyn Cavendish, Duchess of Devonshire (eldest daughter of Henry Petty-Fitzmaurice, 5th Marquess of Lansdowne). In 1938, he succeeded his father as the 10th Duke of Devonshire. They had five children: