pues lo he encontrado y dice así...

The line of the Princes of Dol Amroth, though they were certainly Men, in fact claimed a measure of Elvish blood. It was claimed that the first Prince, Galador, was half-elven: his father was Imrazôr the Númenórean, but his mother was an Elf-maid, Mithrellas. Imrahil was Galador's direct descendant through twenty-one generations, and so could himself claim distant descent from Mithrellas.
Tolkien makes it clear that this was a tradition in Dol Amroth, and not necessarily a true story. According to the legend, Mithrellas was a companion of Nimrodel, who became lost in the woodlands of Belfalas, and was taken in by Imrazôr. As far as they go, these details match the established history of Nimrodel's journey. Unions of Elf and Man, though, are all but unheard of in Tolkien's universe, and are always of vital historical importance. The Princes' claims of Elven descent, while they are not certainly false, are difficult to accept without scepticism.

Esto dice, resumiendo para los que no puedan traducir, que a pesar de que se ha dicho que el antepasado de Imrahil, Galador, era hijo de Imrazor (un hombre numenoriano) y una doncella élfica, Mithrellas. Pero que esto no pasa de ser una tradición de la casa de Dol Amroth y no es una verdad comprobada, puesto que las uniones entre hombres y elfos (las 3 que conocemos) siempre han tenido una importancia histórica trascendente, lo que parece que no es el caso con esta. Por tanto se acepta con mucho esepticismo esta versión (si no es que no se la acepta para nada)
Saludos