Lord of the Rings author JRR Tolkien was heavily influenced by Welsh when creating the Elvish language for his books, an academic says.
Dr Carl Phelpstead of Cardiff University said one language even sounded very Welsh.
He has just completed a study of Tolkien's debt to the language and literature of Wales.
It is being launched at a free public event on Saturday, celebrating Welsh scholarship on Tolkien.
For Tolkien and Wales: Language, Literature and Identity, Dr Phelpstead said he examined a wide range of his fictional and scholarly work.
He said: "He knew the Welsh language extremely well - both medieval and modern Welsh.
"He read a lot of medieval Welsh literature, taught medieval Welsh when he was working at Leeds University and you can see the influence of the language and the literature in his creative writing and his scholarly work."
He added: "Welsh is important as an influence particularly on one of the Elvish languages, Sindarin.
"It's not so much that he borrowed Welsh words, more the sounds.
"This particular Elvish language is very like the sounds of Welsh and deliberately so.
"I have a friend of mine who is a native Welsh speaker who went to see the Lord of the Rings films and when they started speaking Elvish in the film she turned to her daughter and said 'they are speaking Welsh' so people do see this relationship."
Dr Phelpstead said he also had access to Tolkien's unpublished manuscripts and the collection of Welsh books the author owned.
"The marginal comments, corrections and other notes provide interesting evidence of the depth of Tolkien's knowledge of medieval and modern Welsh."
His book will be launched at 1400 BST on Saturday at Cardiff University's Bute Building.
Dr Phelpstead said: "I thought that, given the wide interest in Tolkien's work, it would be worth combining the book launch with some talks explaining and celebrating the influences of Wales and Welsh on his fiction and scholarship."