Hmm, maybe I ought to have it use divine magic rather than arcane. At least some. . . .
It has to be a sorcerer bloodline because the character in question, owing to his royal blood, would never be so irresponsible as to adventure without compulsion, and the law of the land is that all sorcerers must. (To get them out there and probably -- and preferably -- dead.) But owing to the nature of the bloodline, I can build it more easily out of cleric spells. Hey, it's a home-brew world.
And -- the great rule for determining characters' level is what is the highest level spell you need any of them to cast. I'm still narrowing in on that. Especially since the climax will turn on a spell that neither our hero nor our villain cast --
Circling around, that's how you narrow in on defining the character. This one will take a lot of circling.