Wishing you luck! Hopefully this type of experience never happens again, but if it does, don't feel any responsibility to tell your manager where you're going. When employees leave for other roles, it actually helps bad managers' case, because they can say, "We're sad to lose Rachel, but we did such a good job preparing her for [next role]."

If you simply leave to leave, that's more difficult for an ED to explain to a board. (Lots of unfortunate experience with this in my own world!) Even if they eventually know where you're landing, it can be cathartic to make them squirm for a little bit... :)

But again, congrats on the big move and have an easy time settling into the good work.