An unpublished and previously unknown Enid Blyton novel is believed to have turned up in an archive of the late children's author's work.
Mr Tumpy's Caravan is a 180-page fantasy story about a magical caravan.
It was in a collection of manuscripts that was auctioned by the family of Blyton's eldest daughter in September.
"I think it's unique," said Tony Summerfield, head of the Enid Blyton Society. "I don't know of any full-length unpublished Blyton work."
The collection was bought by the Seven Stories children's book centre in Newcastle.
Blyton, who died in 1968, remains a children's favourite and a publishing phenomenon thanks to such characters as the Famous Five, the Secret Seven and Noddy.
An estimated 500 million copies of her books have been sold around the world, with updated and reprinted versions of her most popular stories still selling eight million copies a year.
Mr Tumpy's Caravan follows the adventures of a caravan with feet and a mind of its own.
Together with Mr Tumpy, his friends and a dog called Bun-Dorg, it crosses an ocean before facing a dog-headed dragon in an attempt to save a princess's land.
It was initially believed to have been a version of a picture book called Mr Tumpy and His Caravan, compiled using comic strips published in the London Evening Standard in the 1940s.
Imogen Smallwood, Blyton's youngest daughter, told BBC News: "It does appear to be a little bit of a mystery because there is a Mr Tumpy book that was published in 1949, which was actually a cartoon book.
"I just thought that was that. But no, it turns out that this is completely different.
"It's a whole book, written with words, about a completely different Mr Tumpy and indeed a completely different caravan.
"There's always excitement when an unknown typescript is found of anybody's who is well known," she continued.
"Because this wasn't even known about, it has to rank quite high."
The typescript is not dated but bears the address Old Thatch, Bourne End, Buckinghamshire - Blyton's home until 1938.
The collection of original typescripts was auctioned following the death of Blyton's eldest daughter, Gillian Baverstock, in 2007.
Seven Stories archivist Hannah Green said she realised the typescript did not appear to be closely related to the picture book when she came to catalogue the collection.
"When I looked in more detail into this, it became apparent that it was actually very different and looks like an unpublished novel," she said.
"It doesn't often happen that you have something unpublished by such a well-known author. I think I am probably the first person, certainly in a very long time, to have read the whole thing.
"It was really exciting to spend an afternoon reading it."
Chorion, the company that controls Blyton's estate, said it could not be 100% sure about the differences between the picture book and the novel because they both "pre-date our acquisition of the Blyton Estate".
"However, we have every confidence in the Enid Blyton Society's views," Chorion's Esra Cafer said. "No-one knows more about Blyton's works than Tony Summerfield. This is a great find and Seven Stories is the perfect home for it."
Seven Stories paid around £40,000 for a number of items, including original draft copies of the Famous Five, Secret Seven, Noddy and Malory Towers books.
Combining a gallery, children's activity hub and a preservation centre, Seven Stories aims to save and celebrate great British children's books.
Set up in 2005, it is attempting to establish a national collection of manuscripts and memorabilia from leading authors and illustrators.
Photo of the typescript reproduced with the kind permission of Chorion Rights Limited. Enid Blyton is a registered trade mark of Chorion Rights Limited. All rights reserved.