An early, unpublished work by J.R.R. Tolkien penned before The Hobbit is set to hit bookshelves this spring.

Publisher Houghton Mifflin Harcourt announced Tuesday that Tolkien's The Legend of Siguard and Gudrun, featuring notes by the author's youngest son, Christopher Tolkien, will be released in May.

Tolkien wrote the book, said to be a reworking in verse of old Norse epics, during the 1920s and 1930s while he was teaching at Oxford University.

He published The Hobbit in 1937 and followed with his The Lord of the Rings trilogy. His books have sold more than 200 million copies worldwide.

Tolkien died in 1973, but his son Christopher has helped bring a number of his unfinished or previously unpublished works to the public.

Christopher Tolkien edited and published his father's unfinished work The Simarillion in 1977. He also spent 30 years working on his father's manuscripts for The Children of Hurin (begun in 1918), with the completed tome published in 2007.

With files from the Associated Press