Margaret Rhodes, the first cousin of Queen Elizabeth II, was employed as a secretary to the head of MI6.
"The daughter of the 16th Lord Elphinstone, who was a bridesmaid at the Queen's wedding and still regularly receives visits from Her Majesty, was tasked with reading messages sent from British spies across the globe, narrowly avoided being killed by a V1 rocket, and had her London landlord arrested on suspicion of being a Nazi spy.
She recalled: "I wanted do my bit and went to join the Women's Royal Naval Service, but found myself in MI6. It was dreadfully hush-hush and, for an impressionable 18-year-old, terribly mysterious.
"I reported each day to a disguised office near St James's Park underground station. It was 'Passport Control' on the ground floor, but upstairs we were MI6."
The teenager, who had spent her childhood summers playing with Princess Elizabeth at Balmoral, said the structure of the secret department closely mirrored that of the fictional Secret Intelligence Service (SIS) created by Ian Fleming.
She said: "The big chief, 'M' to James Bond fans, hid behind the letter 'C'.
"He wrote in green ink and God-like powers were attributed to him by us underlings.
"One of my daily tasks was to read every single message transmitted by our spies all over the world.
It was fascinating, but frightening too."