Oceanborn (The Aquarathi #2) by Amalie Howard
The coronation is over.
But the battle has just begun.
Nerissa Marin has won her crown. But can she keep it? Already, her ties to the human realm are driving a wedge between Nerissa and her people. When word arrives that her part-human prince consort, Lo, has been poisoned, she makes the difficult choice to leave Waterfell and return landside. As the royal courts debate her decision, even more disturbing rumors surface: a plot is rising against her, led by someone she least expects.
On land, Nerissa learns another shocking truth: Lo does not remember who she is. As her choice to try to save him threatens her hold on her crown, changing loyalties and uncertainty test her courage in ways she could never have imagined. Nerissa will have one last chance to prove herself as a queen and save the undersea kingdom she loves.