A few of the cast members mentioned in interviews that in some crucial scenes he wasn't even on the set at the same time with the people he was interacting with. They filmed the scenes desperately, sometimes with different actors or just stand ins so he wouldn't even know the full context of a scene he himself was in after filming it. After some slip ups with his first movie they took NO chances.
He very genuinely probably DIDN'T know what was going on until shooting day.