If I could post memes, I'd post the one where a dude was holding up some weird relic and saying "It's been 1000 years...". Because that's how long it's been.
Also, I did read the LN but that was so long ago I can't even remember what happened. But I'm glad they addressed the elephant in the room; The 2nd isekai person. It was foreshadowed early on when Sophia and Katarina first met, as the latter felt some similarity and warmth from Sophia. It reminded her of an old piece of memory that she can't exactly remember fully but that was when her best friend was revealed for the first time.
So yeah, I'm glad this is how it's truly revealed.