Stella Tennant was the granddaughter of Andrew Cavendish (Sir Andrew Robert Buxton Cavendish, 11th Duke of Devonshire ) and Deborah Cavendish (Dame Deborah (nee Mitford) Cavendish, Duchess of Devonshire) on one side and of Lord Glenconner on the other side. Relatives included Colin Tennant (uncle) and Nancy Mitford and Jessica Mitford (great aunts). Tennant eschewed using her hereditary title of "Lady".