Ann Prunella Stack OBE (28 July 1914 – 30 December 2010) was a British fitness pioneer and women's rights activist.
She was head of the Women's League of Health and Beauty which her mother Mary had founded in 1931. In 1953 she led a multiracial team to the coronation in London.
Stack was born in India, the daughter of a Gurkha Rifles officer, Captain Edward Hugh Bagot Stack, and his Irish wife, Mary. At the onset of the First World War in 1914, her father was posted to France, while Stack and her mother embarked on a voyage to England; by the time of their arrival, news had arrived of her father's death in action.
In 1938 she married Lord David Douglas-Hamilton with whom she had two sons, Diarmaid Douglas-Hamilton and Iain Douglas-Hamilton. Douglas-Hamilton, then a squadron leader in the Royal Air Force, was killed in 1944 when his damaged airplane crashed, following enemy action over France.
In 1950, Stack married the surgeon Alistair Albers in South Africa. Albers died in a climbing accident in 1951, while climbing Table Mountain accompanied by his wife. In 1964, she married Brian Power, an Irish barrister.