In one arc of the novel, MC was the first-born son of the emperor but he was disabled, and was thus eliminated as a candidate for the throne. The emperor was sick and they thought MC would use it as a chance to usurp the throne, but he did not, he just used a bit of the power to be in charge. Another prince was being supported by the emperor and was encouraged by the latter to ask help from a general, the ML. When ML met MC, he thought the other was another person, not the current ruler. And lots of misunderstandings happened. The people realized how great MC was and they supported him than the other prince. And ML only found out he was the new emperor when he went to invite him in the palace. Some of the above info might not be as accurate as the original text 'cause I read the novel some time ago. Thanks in advance!