I know people who do indeed have Irish words to the tune of the Fairy Boy and who call it an leana sí. And there would seem to be a similarity with Dónal (one 'l' or two?) Óg in one of the melodic lines.

Very good references from Malcolm which I appreciate. I think Joe Heaney used to sing the Anach Cuain version too, whether he picked it up on his travels or heard it at home.