Childe was a prince, set to be the heir. And ofcourse, he has a fiance, but the duke knows he doesn't love her. As a result, the duke hired you to lecture him about love and whatnot since you were a popular romance novelist, maybe even give him some instructions and tests to help. You don't know what this prince has in store, and to be fair, it is intimidating. You just have to pray he's nice to you.