There is a Threetoe story about a half-elf/half-goblin and her parents, though I doubt the latter's relationship was ever described in that way. But you have a point. Elves (and other fantasy beings) are often described as alluringly beautiful, even to members of other species, and that is a case of cross-species proclivities, just a case not bound to individuals. Being such a common trope, it would be a shame if it didn't make it in. It would technically add some realism too, as IRL humans do definitely not restrict themselves to what is 100% human.
Also I find it really funny. +1
To me there is no question whatsoever that in a fantasy world that stuff would happen all the damn time heh. Hell, I'd probably be getting busy cross species myself, if our world was a fantasy one.
If you haven't, check out Glen Cook's Garrett PI books sometime. He hits the nail on the head about that stuff, like he does with so much other realism in his fantasy. The majority of non-human emigrants in Tun-Fare (sp?) are described as "breeds" (usually in a derogatory manner by the human rights types). Breeds are mixed breeds, because every single sentient creature in that world can cross breed with all the others. Well assuming the sized differences work enough to make that possible.There's three part gnoll part giant characters who claim to be triplet brothers from three different mothers (don't ask, even they don't know how that worked).
Those and his Black Company books have to be the most realistic (in the sense of peoples motivations, actions, ways of speaking etc) fantasy ever put on paper.
Not to mention the Black Company books are hands down the best fantasy ever written.