Katherine and Nerissa Bowes Lyon were born to John Bowes-Lyon and his wife Fenella in 1926 and 1919 respectively.
John, also known as Jock,was the older brother of Elizabeth Bowes-Lyon, who would later become the Queen mother.
While Katherine and Nerissa's siblings, Anne and Diana (who was a bridesmaid to the Queen), were well-known among the high society of the day, Katherine and Nerissa spent the majority of their lives in The Royal Earlswood Institution for Mental Defectives in Surrey.
Katherine and her older sister Nerissa, who were born mentally disabled, were sent to the Royal Earlswood on 5th August 1941, at the ages of 15 and 22.
Katherine and Nerissa, who was categorised as an 'imbecile' in the surviving medical notes, had few visitors at Earlswood and their mother Fenella, who is said to have visited regularly, ended her visits in the 1960s when she died. In 1963, the sisters were listed as dead in Burke's Peerage, the most authoritative guide to the British aristocracy.
By this point, they had spent over 20 years inside Earlswood, which had by now been taken over by the NHS and re-named as the Royal Earlswood Hospital. Nerissa would remain here for 23 years more, until her death in 1986. Nerissa was buried in a grave that was marked with a plastic tag bearing her serial number and name.
In 1987, the existence of the two sisters made front page news but did little to change Katherine's situation. Katherine remained in Earlswood for much of the next decade and then was moved to Ketwin House, a care home for the mentally disabled. The closure of the home due to poor standards meant that Katherine was moved to another care home in Surrey, where she is still believed to be living today.
Katherine's family say that they now continue to be informed about her health via her carers to whom they are grateful.