Since when does he know??

basically during the night the 2nd personality told chipmunk that he would be gone the next day. When morning came the prince went to check up on chipmunk, chipmunk was half asleep and asked why the prince was there when he was supposed to be gone, after asking the question the prince found out that chipmunk and the servants have been lying to him since he never told him before.

I tried my best explaining man