This story started so good but has started to get drilled with plot holes towards the end. ML's Oldman aide basically got his own kingdom attacked to put ML on the thrown and it just got glossed over ? Dude committed treason in such a sloppy way which even had witness from another country, that's a huge weakness to have to hang over a new King's head.
And as another comment pointed out, they basically let the high priest go wherever he wanted in the castle & territory with no tail on him whatsoever despite knowing he is suspicious? That's just asking for the castle to be attacked, even without magic he could have easily leaked the weak points of the castle to enemies.
Just too many dumbass moves are happening back to back.