Vale of Dreams by C.N. Crawford

Nia never imagined becoming the fake mistress of a terrifying Fey prince known as the Dream Stalker. But that’s exactly what happens when she ventures into Brocéliande to rescue her lover, Raphael. Sometimes, fate has a twisted sense of humor.
Captured by the prince, Nia quickly learns he’s a beautiful, living nightmare. He soon discovers her hidden talent—mind control—and gives her no choice but to serve him. Avalon Tower believes it’s a good idea, too. Now, Nia is keeping secrets from everyone, and the Dream Stalker remains unaware that she is a spy. His plan? Manipulate ministers, overthrow his father, and annihilate humanity.
Seductive and complex, the prince is a constant threat, always on the verge of getting inside her head. In the Fey palace, courtly intrigue reigns. If Nia can’t outsmart the prince, her neck will be the next on the execution block, and humanity will be crushed in his beautiful hands.