Shard & Shield. The Shard of Elan, #1

He can save her life-if he sacrifices those he swore to protect. King's bastard Shianan Becknam buries himself in his military career to avoid the dangers of drawing political attention. When the artifact intended to end an interdimensional war is damaged, a mage is trapped on the other side of the rift with her servant-only the cheery young boy is really one of the monstrous enemy, disguised as a human.
Shianan is desperate to rescue Ariana, one of his few friends, but to do so requires committing treason and betraying his people to attack. State mage Ariana struggles to survive as a prisoner of war in a world of deadly magic and unfamiliar customs. Her only ally is her former servant, once again a renowned warrior caught up in political machinations. To survive, he'll have to take up the fight against Ariana's world. As their people's wasted armies prepare for fresh battle, bastard, mage, and monster must set aside prejudices and rivalries to find an end to centuries of conflict, before they die as traitors. Book 1 in a new epic fantasy series The Shard of Elan. This new epic fantasy series by an award-winning author is recommended for fans of Patrick Rothfuss, Brandon Sanderson, and Brent Weeks.