The Bastard Prince — Blair Bancroft

What to do with K'kadi Amund, the youngest of four royal children—the one who doesn't talk? The young man of almost twenty-one who can still lose himself in moments of beauty, or moments of disaster. Unreliable and weird are some of the kinder things said about him. So why does S'sorrokan, leader of the rebellion against the Regulon Empire, consider him one of his most vital assets? But even when K'kadi comes into his own and gets what was once his greatest desire, he discovers that growing up comes with a price.