LORD of the Rings fans can once again immerse themselves in a new JRR Tolkien novel - a century after it was written.

The epic tale of Beren and Lúthien has been painstakingly restored by the author's son, Christopher Tolkien, 92, from manuscripts.

It was written in 1917 after his father returned from France, fresh from the Battle of the Somme.

The story follows the lovers Beren, a mortal man, and Lthien, an immortal Elf.

"Her father, a great Elvish lord, in deep opposition to Beren, imposed on him an impossible task that he must perform before he might wed Lthien", a description from publisher HarperCollins' says.

"It leads to the supremely heroic attempt of Beren and Lthien together to rob the greatest of all evil beings, Melkor, called Morgoth, the Black Enemy, of a Silmaril."

It has not been published in a standalone form before because a version of the story was previously included in the The Silmarillion, a collection of stories and history that Tolkien wrote as background to his Lord of the Rings series. 

HarperCollins added: "To show something of the process whereby this legend of Middle-earth evolved over the years, Chrstopher Tolkien has told the story in his father's own words by giving, first, its original form, and then passages in prose and verse from later texts that illustrate the narrative as it changed.

"Presented together for the first time, they reveal aspects of the story, both in event and in narrative immediacy, that were afterwards lost."