Immortal by Sue Lynn Tan

A young ruler must forge a delicate alliance with the untrustworthy yet magnetic God of War to protect her kingdom in this stunning romantic fantasy filled with dangerous secrets, forbidden magic, and passion, from Sue Lynn Tan, bestselling author of Daughter of the Moon Goddess

The young heir to a mortal crown, Liyen ascends a precarious throne when her grandfather dies, vowing to end her kingdom's obligation to the immortals and take vengeance against those she feels responsible for his death. When she is summoned to the Immortal Realm, she seizes the opportunity to learn their secrets and to form a tenuous alliance to safeguard her people, all with the one she should fear and mistrust the most: the ruthless God of War. As they are drawn together, a treacherous attraction ignites between them--one she has to resist, to not endanger all she is fighting for.

But with darker forces closing in around them, and her kingdom plunged into peril, Liyen must risk everything to save her people from an unspeakable fate, even if it means forging a dangerous bond with the immortal... even if it means losing her heart.