In The Shadows by L.B. August

Damned by gods and threaded by fates, two mortals must embrace the darkness to find their true destinies.

Lilith Clarke is supposed to be dead: murdered by the vicious King Oren, her blood staining a field of daisies. But death would have been merciful.
After years of having no name, she is finally given a title: Queen of Umbra. But it will cost her everything. Lily is now bound to King Asher, the most powerful and brutal shadow divinus in all of Omnia. Forced to rule in secret, she slowly loses herself to the darkness. She fears it will swallow her whole.
Until he arrives, tugging an ancient thread deep within her soul.
Theodore Kincaid seeks justice in Umbra but falls captive to his sworn enemy, the ruthless King Asher. Trapped in the kingdom that killed his beloved, his fate seems sealed until a chance encounter with the secret Queen of Umbra offers him an opportunity he can’t resist.
Theo and the Queen each believe that they are in full control, but neither is prepared for what the fates have in store.
Amidst a realm on the brink of chaos, two souls collide in a heart-wrenching tale of unveiling secrets, conquering the darkness, and igniting a love that could save or destroy.