J.R.R Tolkien’s “The Lord of the Rings” is arguably one of the most widely read works of fiction in the English-speaking world. However, much before the British writer wrote his magnum opus, he penned a much darker tale -- a retelling of a part of the 19th century Finnish epic poem “The Kalevala.”

Now, a century after the young Tolkien wrote -- and left unfinished -- “The Story of Kullervo,” the work will be made accessible to the general public. The short story, describing the trials and tribulations of the “hapless Kullervo” -- as Tolkien reportedly described the tragic hero of the poem -- will be published by Harper Collins in the U.K. Thursday and in the U.S. on Oct. 27.

“We could say that Tolkien is finding his feet. He ultimately leaves the story to one side without finishing it, switching to write more personal and original works,” Vincent Ferre, professor of comparative literature at University Paris Est-Créteil and a Tolkien expert, told Agence France-Presse (AFP) Wednesday.

Kullervo’s tale is just one of 50 songs in the Kalevala -- a compilation of Finnish and Karelian folklore. The song tells the story of an ill-fated hero who is raised by his parents’ killers and sold into slavery before he unknowingly seduces and has sexual relations with his sister. After she finds out he was her own brother, she commits suicide, driving a grief-stricken Kullervo to hurl himself on his own blade.

“He was very much taken by the whole mythology,” Verlyn Flieger from the University of Maryland, who edited Tolkien’s manuscript, which first appeared in the academic journal “Tolkien Studies” in 2010, told the BBC. “In his letters he enthuses about this ‘very great story’.”

This is believed to be the first prose piece by the Lord of the Rings author, who had, until then restricted himself to composing poems.

And, according to Flieger, the story served as a precursor to all his later works. In “The Silmarillion,” -- which was begun in 1914 but only published after his death -- Kullervo’s place is taken by Turin Turambar -- son to a father who falls victim to a powerful enemy, and who is drawn into an incestuous relationship with his sister.

However, Tolkien’s version of the Finnish myth -- written in 1914 when he was still a student at the University of Oxford -- is only 26 pages long, reportedly breaking off in the middle of a sentence.

“He had just got to the climax, the most dramatic scene, and it stops. There is no full stop, no continuation of any kind. Only the words ‘so terrible his haste’...,” Flieger told the BBC.