Wow. That’s enlightening. I loved ‘The Mists of Avalon’ when I read it, I was probably 20. I knew it was very risque but didn’t think that much about it, I actually enjoyed the story. But I was and am a King Arthur fan - T.H. White, Jack Whyte, Persia Woolley, Bernard Cornwell, etc. And one author who emphasized the Merlin narrative, I cannot recall the name right now. I just loved the various takes on the tale. Shocks me about MZB. You just never know what dark skeletons are lurking in some people’s closets.
I think Mary Stewart is the author of the “Merlin-based” Arthurian stories you were trying to remember. She wrote 4 books on it, beginning with “The Crystal Cave”. She’s one of my fave writers.
The audiobook version of Moira Greyland’s “The Last Closet” is out.
https://arkhavencomics.com/product/the-last-closet-audiobook/