Somehow i felt that emperor didnt die and just change his identity (or not). By the time hyuk sing i can see sunny face kinda bothered with him ( 0:42 ) and when hyuk said that him being hardcore fans and smile when he call her sunbae-nim probably just to tease sunny . the idea of him survived and change his identity, like they kill the emperor but not lee hyuk, and then he repent being regular person for sunny then trying to win over her heart as again.
This is just my opinion.
is hard for me to see if he's just hyuk dopple. even tho there some cases that its atually
happen ( meaning there will be chance that we had a dopple) then again, the resemblance of him is far to perfect for just coincidence.
i bet they ( sunny, musical director, staff, etc) already know that it was him.