It came to light through the Letters Of Our Lives campaign, an appeal for people to look for letters or postcards giving personal accounts of life in the UK through the centuries.

The letter from Nina Fawcett reveals how she was coping with the disappearance of her husband and son in 1925.

Colonel Fawcett and his son vanished while trying to find an ancient lost city in the Amazon.

The newly released letter was submitted by Rebecca Maltby, who found it in a sewing machine in a house she bought in London.

It is dated January 7, 1926 and was written nearly a year after the final correspondence with the exploration party was received.

Mrs Fawcett writes to Alfred Vout Peters, a famous clairvoyant, to ask for a "psychometric reading by post", and that the reading offers "information and advice as to the family in general, contact with the exploring party and helpful advice" for her young daughter.

She closes by saying that she is "thankful to say [that her and her daughter] both feel quite cheerful" and that "this first year of waiting has passed very quickly".

Ms Maltby said: "When I found the letter there were enough facts to research online. We came across the extraordinary story of Colonel Percy Fawcett's hunt for the City of Gold, his presumed death, the 100 people who have died looking for him, and how Nina continued to believe she was in psychic contact with him for 25 years after he disappeared.

"It was, and continues to be, such an exciting treasure hunt of a letter to investigate."