@cor3zone
News takes a while to reach the ears of the king. Even then, information could be controlled since the perpetrators are inside the country. 500 men marching into the forest? Nope, we didn't see anything like that.
Dismissing the soldier tho was really dumb. It's convenient for the landlord and to move the plot forward, but makes the competence of the prince and his supporters inconsistent. Maybe it's part of the plan? The hooded guy mentioned something about a plan.
I doubt that the king is conspiring with the prince since he has already rejected the prince's suggestion to retaliate. The conspiracy is being done behind the king, and I bet the prince is just being manipulated (that hooded guy seems suspicious).
The noble doesn't have to be foreign, but they didn't need to be on the same side as the king either. They're in it for glory and renown. The king can't always know what all his subjects are doing.
@flannan
Not every warband has to be affiliated with the kingdom to be needing approval of the king to move around
Even if that warband was deemed to be a threat that needs subjugating, 500 is a large number, and it would take a while to muster enough men and prepare enough supplies to feasibly subjugate a force of that size