The entire story is a self-indulent AU, but I used the "Amroth and Nimrodel," section from Unfinished Tales for reference.
On the the Elvish strain among men
There are numerous references to the Elvish strain among men in Unfinished Tales. Christopher Tolkien says in one note:
"…among the last writings of my father's on the subject of Middle-earth, there is a discussion of the Elvish strain in Men, as to its being observable in the beardlessness of those who were so descended (it was a characteristic of all Elves to be beardless); and it is here noted in connection with the princely house of Dol Amroth that "this line had a special Elvish strain, according to its own legends…."
There are two well-known references to the subject in The Lord of the Rings, of course, both of which issued from Legolas. In The Fellowship of the Ring, Legolas sings the song of Amroth and Nimrodel and then speaks of "the Bay of Belfalas, whence the Elves of Lórien set sail." Later there is the much-quoted one in The Return of the King, where when Legolas first encounters Prince Imrahil of Dol Amroth, he comments that:
"At length they came to the Prince Imrahil, and Legolas looked at him and bowed low; for he saw that here indeed was one who had elven-blood in his veins. 'Hail, lord!' he said. 'It is long since the people of Nimrodel left the woodlands of Lórien, and yet still one may see that not all sailed from Amroth's haven west over water.'
'So it is said in the lore of my land,' said the Prince…"