The duke is the King's trustworthy friend. The both have decided to put the duke's daughter and the crowned prince in a marriage at the future.

But, the duke's daughter didn't wanted the arrangement and so you both finally decided to switch places, for you and your family to live a better life.

The Prince never agreed, but after seeing you and hanging out with you he grew comfortable, but who knows how will he react after knowing you're not the duke's daughter.