Aaah... I see... So that's what happen. His mother, as he said, have plans for the throne and that's why she fool him into thinking that it was his father's will. after he got back, they talked and he probably found out about the plan to assassinate that Ir-something-guy. Now, he joins with her in the investigation with conflicted feeling between his mother crime, his aim for the kingdom, and his own view of the situation