The Sorcerer and the Swan Princess by Lucy Tempest

A usurped princess. A mercenary sorcerer. A fate neither expected.

As a crown princess, Ava has always anticipated betrayals—but never from her own twin.The unspeakable treachery comes the night Ava meets her true love, when Lina hires the infamous sorcerer, Lord Von Rothbart, to turn Ava into a swan, and takes her place.
Kept across the mountains in Dietrich’s castle lake, Ava’s repeated attempts to escape, to return to her prince and life, keep failing. But in the last time Dietrich recaptures her, she gets close enough to glimpse the terrible truth of what she left behind—starting with that of her prince.
Yet, it’s Dietrich’s true motivations and the unique bond that forms between them that shock her the most.
Will she reject their burgeoning feelings and trust to undo his efforts and reclaim her kingdom? Will he risk the consequences of freeing her from his curse? Will their love survive the demands of duty, and the toll of resentment and threats? Or will it fade away with the moonlight at sunrise?