Stolen Songbird by Danielle L. Jensen

Centuries ago, the Isle of Light was ruled by cruel creatures with dangerous magic until a witch bound them to their underground city. But a prophesy has spoken of a union with a human girl that has the power to set them free.
Cécile is a singer destined for the stage when she is kidnapped and bonded to the cursed prince of Trollus, with their minds linked in a way she never dreamed possible. Trollus is both magical and deadly, but as Cécile hunts for a way to escape, she discovers there is more to her mysterious husband than anyone realizes.
As tension brews and political games escalate, Cécile finds herself at the center of a rebellion… and she is the one with the magic needed to overthrow the tyrant who rules.

Torn between returning to her human life and becoming the princess Trollus needs, Cécile must decide which world she belongs to… and how far she’s willing to go to save the prince who holds her heart.