Yes. Very near the end of the series. I don't have that set yet, but I know the plan.
Though you can start to put parts of it together already, if you pay attention to the books so far. Others have worked out more, of course... (People from other worlds.)
Not a lot though, so, no you probably won't just guess at it.
It's big enough I don't want to give it away until near the end. Also, of course, once that kind of thing is known, it will forever alter the tone of the series in the minds of the readers. So, it'd for the best that I don't say yet.