The Treasure Island author's fairytales are finally to be published in one set, as he intended

The literary betrayal of one of the most popular writers in the English language, Robert Louis Stevenson, is to be avenged in the first collected edition of the great Scottish writer's little-known Samoan fairytales.

Stevenson, the author of the classic adventures Treasure Island and The Strange Case of Dr Jekyll and Mr Hyde, spent the last years of his life on the Samoan island of Upolu where he wrote a series of fantastic tales and fables that he specifically asked to be published as a set.

However, instead of complying with the writer's request, his literary agent, Sidney Colvin, asked Cassell to publish two of the fairy stories – The Bottle Imp and The Isle of Voices – in a volume alongside a naturalistic short story of a completely different type.

"Colvin, his supposed friend back home, stitched him up. He decided they should be published together because he thought he knew what was best and what would make the most money," said Bill Gray, professor of literary history at Chichester University.

Gray, who is also director of the university's Sussex Centre for Folklore, Fairy Tales and Fantasy, has campaigned for six years to have Colvin's decision remedied.

"Stevenson wrote that 'on no account should these stories appear together' in his letter to Colvin and he underlined the point," he said. "Colvin deliberately did exactly what he said he didn't want and then it was all put down to communications problems."

"It took weeks, if not months, to get a reply from Samoa because all the post had to come via Australia."

The two stories have appeared in a volume entitled Island Nights' Entertainment for more than a century and are now to appear in a new edition along with another fairytale, The Waif Woman. This third story was originally dropped by Colvin, but had been intended as a proper companion piece.

Following literary arguments put forward in a conference paper given by Gray in Edinburgh, the city's University Press is to publish a fresh edition of Stevenson's fairytales. Some of Stevenson's fables were published in 1896, but Gray's edition will be the first time they have all appeared together and in the order Stevenson wanted, based on the original manuscripts which are housed in the British Library and the Beinecke Rare Book and Manuscript Library at Yale University.

Gray believes it will be the closest thing yet to what Stevenson had planned before his death in 1894: "It will be the first time they have been read together as a group, just as Stevenson intended."

In 1890, the well-travelled but ailing author, who had suffered with respiratory problems since childhood, bought 400 acres in the village of Vailima. He adopted the native name Tusitala, which is Samoan for "teller of tales".

Stevenson is currently one of the 30 most translated authors in the world and Gray points out that the publication will provide a chance for the Scot to reclaim his reputation as a fabulist, and not just an adventure writer, at a time when fairytales are once again becoming fashionable.

Gray has been appointed as consultant on the Universal Pictures production of Snow White and the Huntsman. Based on the Grimm fairytale, Snow White is to be shot late this summer and will star Kristen Stewart, Joel Edgerton and Charlize Theron.

The new volume of Fables and Fairy Tales is due out in 2013, as part of the New Edinburgh edition of Stevenson's works, which is planned to be the definitive collection.