Ch36
Ruthless 7th prince (leads army) conquered the nearby kingdom, sent the princesses to the king (father) but took the 3rd, unknown princess (5yo born from a maid) for himself. He finds her defiance and cleverness enjoyable, and spoils her in a tsundere kind of way.
*idk what’s up with the marriage/romance genre tags, so far seems to have more of a protective/fatherly relationship.
Prince Bastard’s Parenting Book