The Royal Tutor Vol. 8 (manga)

Kai makes a friend at school and invites him over to the palace for tea. He asks his brothers for help in making conversation, but is that really such a good idea...? Then it's a battle of wits when Heine joins the princes (and princess!) for a game in the courtyard. After all the time they've now spent under his tutelage, can the students finally overcome the master?