An early edition of Magna Carta has been found in a Victorian scrapbook during a search of a council's archives
The discovery has come months ahead of the 800th anniversary of the sealing of Magna Carta in Runnymede in 1215.
Kent archivist Dr Mark Bateson had been asked to search for another charter from the town of Sandwich.
Dr Bateson found the town's Charter of the Forest in a Victorian scrapbook in Kent County Council archives - with the long-forgotten Magna Carta edition.
The document was ripped with about a third missing but could still be worth up to £10m, according to Professor Nicholas Vincent, a specialist in medieval history from the University of East Anglia.
Its high value comes from the fact that it was found with the Charter of the Forest. The only other such pair - dating from 1300 - in the world is owned by Oriel College, Oxford.