Prince in Hiding - Book 1 of The Making of a Mage King Series. The Making of a Mage King series, #2

As sixteen-year-old Sean competes in a tournament with his chosen blade, his mother was killed under suspicious circumstances, there being no detectable reason for her death. After his father's death a little more than a year later, Sean's life took a drastic turn. He found out that he was the rightful heir to a crown on some other world or in some other dimension - the relationship between Ruhin and Earth is unknown - he also learned that his parents weren't really his parents; they had been his mother's personal maid and her bodyguard.
Sean also learns that he should be very strong in magic, and his lessons in that would begin immediately. With both of the people he had known as his parents now dead, he needed to be able to protect himself, and since those two deaths came so close together, Sean's hiding place on Earth must have been found out. It was time to go back and confront the uncle who had taken everything away from him.
He'd taken a life he might have had as a prince of Ruhin, and now he'd taken the life he had on Earth. When he reached Ruhin, he couldn't just walk into the palace and say gimme. He had to master the magic in his blood, and then he had to master the stones. Along the way he had to become known and rally support. He met an old woman who gave him a flag, and using magic, he started to display it wherever he went.
The effect wasn't quite what anyone imagined, but it worked. People by the thousands converged on the capital veiled as if for death. Under cover of the chaos, Sean was snatched by the king, only he discovered that his nephew wasn't so easily tortured into submission.