The Secret Prince by D. Anne Love
The old man Morwid was once the King's counselor but when Kelhadden fell to Ranulf, the Morwid fled the city. No one was safe from the evil ways of Ranulf so the people of Kelhadden flee to the forest in fear of their lives. Morwid sought shelter in the caves on the outskirts of the city living a solitary existance waiting for the prophecy in the book of Ancients to come true.
Finally one day a baby was left at the entrance to Morwids cave and this baby was the promised prince of Kelhadden. It was Morwid's task to teach the baby Thorn all of the things that he will need to become king of Kelhadden. From the first day Thorn does not know that he is supposed to be king only that Morwid is his teacher. So the preparation begins for the time when Thorn will be ready to undergo his quest that will restore him to his rightful place in the world.
When Morwid tells Thorn that he must seek the amulet that was lost and now that the time has come to leave him Thorn has mixed emotions. Thorn begins his quest the very next day and meets friends and foes along the way. He through much trial and evil manages to recover the amulet only to find that the person whom he trusted the most will try and take it from him.