I nominate
The King of Elfland's Daughter by the Anglo-Irish writer Lord Dunsany. You can find it right here in the mobile read library.
https://www.mobileread.com/forums/showthread.php?t=36673
In addition there is an excellent general review of the novel from which I will give the following excerpt:
"Much of what we call modern fantasy is a pale, predictable mesh of cliches. It is a bookshelf filled with stories that bear far too much in common with one another. Sometimes indeed it feels that originality, which ought to be the cornerstone of fantasy seems to be all but evaporated. Lord Dunsay is - different. He is one of those illusive pre-Tolkien fantasy writers and you will be shocked at how much of modern fantasy derives from him. And then doubly shocked to find he still did it better. Lord Dunsay writes beautiful and elaborate prose. He weaves stories in which magic is not some work-a-day technology but rather a brooding, powerful and very nearly living force."
From the novel blurb:
"Alveric, Prince of Erl, ventured off through the mists and brought back with hum Lirazel, the shining daughter of the King of Elfland.
"This was an auspicious beginning. But Lirazel was elf, not mortal. There was no malice in her but neither was she suited to the limited ways of man. No elf could ever be
content. And certainly not in the fields we know. . ."