His Last Name - Tales of Espar, #1

The wizard works alone. She was his one exception. Before Master Kitable appeared in Galanth at the age of thirteen, he'd been a complete unknown. Even twenty years later, he is still only "Master Kitable, " a man without a last name, a wizard without history. He operated in the shadows for the Prince of Galanth when the borders were drawn, then helped the legendary King Tohmas take over Espar. Now, he enforces their tentative unity by policing wizard magic across the kingdom.
His offer to take Shimmer Weaver on as an apprentice after the war was unprecedented. She doesn't fit in the new structure of government; she's a dancer, an apothecary, and a free spirit at odds with their regimented world. But she's also brilliant, and after two years, Kitable has to accept that her apprenticeship is ending. There's only one more mission: a run-of-the-mill investigation of some minor magical issues in an unremarkable corner of Espar.
Only this time, the enemy is Kitable's past hunting him down, seeking to destroy everything he has built, including that which he values most: Shimmer's loyalty.