The mystery letter of Kimbolton, which puzzled people for nearly 40 years, has finally been opened and the author was someone nobody expected.

Carey King, great-granddaughter of the letter's recipient, travelled to Kimbolton to receive the message after an appeal by The Hunts Post on June 25 for relatives to come forward.

The letter sent to Frances Agnes Carter on August 16 1921 from France has been in the possession of retired antique restorer Owen Spice following a Kimbolton house clearance in 1976.

Mrs King, who mainly lives in Pakistan, received the letter along with photographs belonging to the family after meeting Mr Spice and soon peeled open the 93-year-old envelope.

Mr Spice requested that the letter only be opened by a direct relative of the family and said he had never been tempted to read it as it was not his to open.

After reading the letter, Mrs King said: “It's from somebody who was not related, sent as a letter of condolence after the death of Joseph Fabian and the strange thing is the address given was a London one.”

Joseph Fabian Carter, a land agent to the Duke of Manchester, was the husband of Mrs Carter and died on August 11 1921, four days before the letter was written.

The letter was sent from Alice Derby and, although sent from France, was addressed from Derby House in Stratford Place, London.

“The whole idea of a letter not being opened was so peculiar,” said Mrs King, “I should have thought it was not opened because of oversight, as a lot of letters would have arrived and they were in distress.”

Only after leaving Kimbolton did Mrs King realise who the author of the letter was.

She told The Hunts Post: “Alice Derby of Derby House was obviously Lady Derby, wife of the Earl of Derby. Her father was the Duke of Manchester, so of course she knew Kimbolton and the Duke's land agent from her childhood.”

Growing up in Kimbolton Castle, Alice Montagu married the Earl of Derby who was later the war secretary during WWI between 1916-1918.

The couple later moved to France as the Earl became British ambassador for France after the war.

Lady Derby knew Mr Carter from her childhood and said he was “so greatly like by all of us and connected with our early days.”

Mr Spice said he was very pleased with the outcome as he has a great interest in WWI.

Mrs King now holds the letter, along with the pictures, which ends the 38-year search for the Carter family.