Rather than just forgiving him like that, first, MC should have made him apologize to every adventurer he treated the same as the way he treated MC one by one, and in public after making investigations about the truth about them and making expositions about his mistakes first.
This will make him think twice about doing the same things in the future and prevent others from doing the same as him. Complete humiliation and pride-shattering.
Only after that his apologies to the MC could be accepted by the MC and no lèse majesté could be said.