I found it.
Palimpsest by Tais Teng
Dragon Magazine 123 pp 62 July 1987.
She waited just outside the gate. His mother seemed older than the last time, her face a furrowed field, grey invading her black tresses. Or it might be just the merciless glare of the sun, which hid nothing and always seemed intent on highlighting the world's imperfections.
She eyed his pale body with some distaste, noticing that the white of his eyes had acquired the slightest tinge of elfish blue. "I see you have learned to fear the sun."
He shook his head, but not in negation. "Why do you keep troubling me, Mother? I'm happy here. Almost. At least happier than I would have been grubbing the earth in your village. I'm learning important things."
She tried to smile. "Elf magic. I suppose that's quite fascinating. Still, they wouldn't show a mere human the truly important things."
"They hide nothing! I'm one of them!"
"Ah. Even so, there are secrets they wouldn't care to show a human changeling."
Last paragraphs of the story:
The sky turned a dull red, and the temperature dropped sharply. He halted. He knew too well what he would find outside. Only the nuclear Fimbul winter, the empty ruins
Raising his hands, he noticed that they had already grown quite transparent. If only she could have forgiven, he thought. And then, with melancholy curiosity, for he had become more than half-elf, I wonder what the Hand will write next. . . .
Does that sound like it?
EDIT: From your comment above, I am now sure this is it, given this passage.
They murdered Earl Magember and all of his followers. The elfhill is blighted for a thousand years. I suppose they had some justification for their crimes. The reign of my son seems to have been needlessly harsh. The Unnamed gave us dominion over the Garden of Eden, over the mute animals and the animals that speak and feel. Were meant to be the gardeners of men, and according
to the testimony of the dead, Earl Magember behaved more like a wolverine.
You come in the rough glare of burning firs. The humblest tree, fit only for trolls and mortals. You carry iron fashioned from the bones of the First Hag. You come to take my life.