My protagonist is a prince who was imprisoned by his uncle after his father died. This should happen at an age when he can vaguely remember his parents and the life he had. He should be extroverted and sociable, but struggle with socialization, because his contact with people was restricted for a long time. He should have some narcisstic tendencies, mainly the need for approval and black-and white thinking. He will genuinely care for other characters, but ultimately the trauma, distrust, fear need for approval will make him focus more and more on getting the throne and the wealth and power that comes with it.
The question is, what conditions of the prison could create a power-hungry narcisstic teen who can hardly relate to other people, but his intellect and social instincts are preserved? How long would the imprisonment "ideally" last and from what age?
Some info that might be relevant: His uncle (the king) killed his father and stole his throne. The prince knows it and hates the king deeply. The king resents ruling. He murdered his brother because he was destroying the country with his incompetence and he saw it as his moral duty to do whatever necessary to save it. They never liked each other, but even though the king wouldn't admit it, the murder weights a lot on his conscience. He hid the prince away because he would likely turn out the same as his father, but adopted his younger sister, who could still be "raised well" and couldn't inherit the throne anyway. The prince escapes/is freed as a teenager, max. 20 years old.