Ace's Plan

Ace decided to tell his secret as it will be very difficult to lie with these people who were aware of his Divine Sense and his Void Phase that he can no longer use. There was also his Astral Core which ultimately given him a different form of energy that he can no longer show. 

These people were sensitive to foreign energies so it will be hard to trick them with mere words.

In fact, there was not a single hint of such energy within his body so these people who had joined him in the operation would easily identify the difference.

He can tell them that many things had changed after going to the northern continent but aside from that, he was also unsure of what more to say about the events that truly happened when 'he' decided to be left behind in that tower. 

 "Well, so that's the reason why I'm unsure what happened to my Master as well... Right, can we keep this a secret?"