I don’t think it was the crown prince, bc if they revealed it at the end if the chapter so easily than there wouldn’t have been a reason to disguise that person in the first place.
I bet is the Duke, since the og FL said he return back with a dark face , I guess he can't find the MC
Possible theory (・o・)
Or prince witnessed the duke did naughty things to Maythan and chose to leave silently
That's possible too
ハハハッハッハ I thought it's was the Duke (the supporting ml no2) I even go back to the chapter 1 just to identify who was that man and then it was the crown prince ( ꈍᴗꈍ)