Brutal Dictator

A long time ago, in a country far away, the King sentenced a man to death. He told the
man, “You shall be shot at dawn, one day next week. However, the evening before
you are shot, you will not know that you are going to be shot the next day.”

While the King was a brutal dictator, he never told a lie. The condemned man proved
that it was impossible for him to be executed.

How did he do this and was he correct? [hint: what is the last day he could be shot?]