Mesmer, Book 3: The Amarinth Heir (A Three Towers Fantasy‪)‬

In the stunning conclusion to this YA romantic fantasy trilogy, sword and sorcery collide with shocking consequences for the fate of the three kingdoms...
When Gabriel Amarinth granted Lea Tornith sanctuary in his magical kingdom of Verlaine, neither foresaw the discovery of a secret hidden long ago by an ancient enemy, a secret that could alter the fabric of Lea and Gabriel’s very different worlds forever. Now, the Lorien spy must make a choice: protect the kingdom she never believed she could betray, or save the realm—and mage—she never thought she could come to love.