that dialofue from GF3 makes that clear, but even if Part III was never done, I would still think that Kay knew about Appolonia. I think Turnbull got the point (surprise!).

Michael probably wanted to be straight to Kay, and he would be such a stupid if he kept Kay in the mall and still tried to hide such an important thing from her, knowing that someone could acidentally let her know the truth.

btw, I have an off-topic question:
Turnbull, why do you only post in the Godfather-related threads? (at least is only where I see you) well, I'm just curious.