Your Majesty, My New Father

Ethan's father is the emperor's brother, which nobody tells Ethan until well after he has stopped needing to know. Ethan places first in the imperial examination, and at the audience that follows he addresses the emperor as "Father". The emperor lets it pass. He had already decided to marry Ethan to the princess before the summons went out, so the slip costs Ethan nothing. Then Ethan sees the princess, who is ugly, and the decree has already been issued. He cannot refuse it. He accepts the marriage and lives with what he has been given, and the fact about his father comes to him afterward.