Two of four daughters of John Bowes-Lyon (the Queen Mother's older brother), Nerissa and Katherine Bowes-Lyon were born in 1919 and 1926; Katherine is only three months younger than her cousin Elizabeth, the girl who would one day be crowned Queen.
From the ages of 15 and 22, respectively, they were sent to live at the Royal Earlswood Hospital, an institution for the learning disabled in Surrey, which was built in 1855 as an 'Asylum for Idiots'.
While their two other sisters enjoyed lives of privilege and inclusion in the social world of the aristocracy and the royal family, Katherine and Nerissa were all but forgotten.
The two sisters seemed to be aware of their royal connections; when royal events were shown on television, they would curtsy to the screen.
In 1963, Burke's Peerage, the guidebook to aristocratic lineage, recorded the sisters as having died in 1940 and 1961. Nerissa actually died in 1986, and Katherine was moved into a home in the community when the Royal Earlswood was closed down in 1997.
The film explores the harsh realities of life inside former asylums like the Royal Earlswood through the personal testimony of former residents, their families and the staff who worked there and cared for the Queen's cousins.
Through their accounts, and with the insight of medical historians, the programme examines the changing attitudes to learning disability in British society.