The majority of the early army is former soldiers of Prince Stromage. Basically, his and the king personal guard.
The power that King Brian has is the army. He lets them do what they want with the people, and provides them with plenty of money for their loyalty. He is a cruel, cunning leader.
Hmm, Prince Stromage is a slightly proud, a leader who draws people to him, and an excellent soldier. If anything that would hurt him is his impatiences. Their in lies Red, his comrade who is patient, a better general and soldier but not a leader. They check and balance each other.... sort of. Red also is much harsher and a better judge of character will Stromage is well more idealist.
At the beginning of the RPG, the work will be secret. No will know that the Prince or Red survived from the King's Guard, or that some of the army that supported the king fled with them. From there it must be decided.