Nerissa Jane Irene Bowes-Lyon (February 18, 1919 - 1986) was a niece of Queen Elizabeth the Queen Mother and a first cousin of Queen Elizabeth II. She came to the attention of the public when it became known that although she was described as having died in 1940 by "Burke's Peerage," Bowes-Lyon actually was alive and well, though mentally retarded and confined to various institutions since 1941.

A daughter of the Honorable John Herbert Bowes-Lyon (died 1930) and his wife, the Honorable Fenella Hepburn-Stewart-Forbes-Trefusis (died 1966), Nerissa and her sister Katherine Bowes-Lyon were born mentally retarded. When Nerissa was 22 and Katherine was 15, they were removed from their family home and placed in a psychiatric hospital - Royal Earlswood Hospital in Surrey - where Nerissa spent the next 46 years. The sisters reportedly had the mental age of six and were largely unable to speak. They had a sister who was born without any handicaps, the socialite Diana Cinderella Mildred Bowes-Lyon, Mrs. Peter Somervell (1923-1986); she was a bridesmaid at the wedding of Queen Elizabeth II.

The Royal Family informed Burke's Peerage, in a calculated fabrication, that Nerissa Bowes-Lyon had died in 1940. When it became apparent that this was not the case the editor of the book responded, "if that is what members of the family told us, then we would have included it. It is not normal to doubt the word of members of the royal family."

Three of the Bowes-Lyon sisters' cousins were institutionalized as well, all classified as mentally disturbed: Idonea, Etheldreda, and Rosemary Fane.

Nerissa Bowes-Lyon was buried in Redhill cemetery where her grave was marked with a plastic tag and a serial number, though a headstone has now been placed there.