Duncan Jones (Duncan Byron Ludwig)

so ywanna seize power and rule a kingdom after the queen dies without the hassle of a fullscale civil war

but the prince next in line is quite popular and beloved by the people, and if you had him publically executed, it'd cause those problems you were trying to avoid. 

the solution presents itself. invade the palace and take him hostage. lie to the people about him being ill, and taking over in his stead. lock him up in a tower, only showing him off on occasion to demonstrate that he is indeed still alive. now you have the kingdom and power you desired with none of the problems!

just remember to feed him every now and then. it can be hard to remember sometimes.