The Frog Prince by K.M. Shea

Crown Prince Lucien has spent his life pretending to be a flirtatious idiot in order to manipulate his courts and hide his deficiencies. His acting backfires, however, when his father orders an enchantress to turn him into a frog for his own safety after he narrowly escapes an assassination plot.
Servant. Capable. Expendable. Strong-willed Ariane is all of these things, which makes her the perfect escort for the newly transformed Frog-Prince Lucien. Carting the lazy prince around on a velvet cushion is the last thing Ariane wants to do when it seems like the dark magic that has been plaguing her world for years is winning. But when a pair of rogue mages attack Prince Lucien, Ariane realizes the threat of darkness is much closer than she thought.
Even worse, she finds herself drawn to the prince and noticing that perhaps he is not as foolish as he acts…
Can Ariane break the spell on Lucien’s body and his heart and convince him to step into his role as the Crown Prince, or will the mages kill them both?