The Doll, billed as "a dark story of obsession and jealousy", is the peculiar tale of a man who becomes infatuated with a woman he meets at a party. He visits her home only to discover the real object of her affection: a life-size, mechanical male doll.
The story was written around 1928 and the female character was called Rebecca, a name Daphne du Maurier would use a decade later in her most famous novel. It is one of 13 du Maurier short stories to be published in a new anthology.
The author made reference to The Doll in her autobiography but biographers and academics failed to find it.
Ann Willmore, a du Maurier enthusiast, spent years on the case and finally unearthed it in a 1937 compendium, The Editor Regrets, of stories that had been rejected for publication.
Mrs Willmore runs the Bookends bookshop in du Maurier's hometown of Fowey, Cornwall. "I have had a long interest in Daphne du Maurier and I collect examples of her work from old magazines or journals in the UK or America.
"It was by complete chance that I was searching online one day and found The Editor Regrets. Realising what I had found was very exciting and it was just luck."
Mrs Willmore discovered five of the 13 stories in the collection, entitled The Doll, which will be published by Virago in May. They include a ghost story, The Happy Valley, which is set in Cornwall and also presages Rebecca.
Du Maurier died in 1989. Her son, Kits Browning, said The Doll story was "riveting and quite ahead of its time".
"I only wish it had been discovered when my mother was still alive," he said. "It's a very dark and disturbing story for someone who was 21 when she wrote it, and from the sort of background she came from. It's all about a male sex doll.
"I would have loved to have teased her about it," he added.