Warning, spoilers for The Elder Scrolls Online: Necrom.
The Elder Scrolls Online's newest expansion just launched, and because of the PTS from earlier this year and dedicated players who have run through much of the story already, we know about a major plot twist that shakes up TES lore in a way we haven't seen since Oblivion.
There's a new Daedric Prince - Ithelia, otherwise known as The Prince of Paths, The Mistress of the Untraveled Road, The Fate-Changed, and The Unseen.
Hermaeus Mora is the focus of the chapter but, during the story, it's revealed that most of the Princes we know banded together to take down Ithelia and subsequently erase all knowledge of her existence.
It's unclear if she held the title of The Unseen before this event, but if she did, it would be a twisted fate of irony. But it's not unprecedented, and neither is the idea of a hidden Daedric Prince. Oblivion's Shivering Isles DLC saw the return of Jyggalag, the Daedric Prince of Order.
Like with Ithelia, the other Princes banded together to take down Jyggalag for fear of his immense power. They cursed him to become Sheogorath, the Daedric Prince of Madness, a punishment laced with irony much like Ithelia's. However, every so often, he has the chance to return and reclaim his place. He tries this in Shivering Isles, but we - the Hero of Kvatch - stop him, and it's even believed we become Sheogorath in the process.
The difference between the two is that Ithelia is a completely unexpected reveal. There was no evidence of another Daedric Prince after TES4, whereas Jygallag was mentioned in the On Oblivion book that first appeared in Morrowind. Daggerfall lead designer Ted Peterson says his name was added just in case Bethesda needed another Daedric Prince in future games, and they swiftly brought him into play in the very next instalment.
Ithelia was wiped from history, however, so ESO has a good in-universe explanation as to why we haven't heard of them.
In Necrom, we find out about her thanks to a forlorn former servant, Torvesard, who tells us, "There was another Daedric Prince! My Prince! A Prince that saved me and preserved just enough of my memory so that I could one day save them in return. A prince whose jealous and craven siblings cast down and wiped from the annals of history."
Evidently, the memory of her is important to keep her alive, and with the knowledge of her bleeding back into Nirn, perhaps there's room for a return.