The Guinevere Deception by Kiersten White

There was nothing in the world as magical and terrifying as a girl.

Princess Guinevere has come to Camelot to wed a stranger: the charismatic King Arthur. With magic clawing at the kingdom’s borders, the great wizard Merlin conjured a solution–send in Guinevere to be Arthur’s wife . . . and his protector from those who want to see the young king’s idyllic city fail. The catch? Guinevere’s real name–and her true identity–is a secret. She is a changeling, a girl who has given up everything to protect Camelot.

To keep Arthur safe, Guinevere must navigate a court in which the old–including Arthur’s own family–demand things continue as they have been, and the new–those drawn by the dream of Camelot–fight for a better way to live. And always, in the green hearts of forests and the black depths of lakes, magic lies in wait to reclaim the land. Arthur’s knights believe they are strong enough to face any threat, but Guinevere knows it will take more than swords to keep Camelot free.

Deadly jousts, duplicitous knights, and forbidden romances are nothing compared to the greatest threat of all: the girl with the long black hair, riding on horseback through the dark woods toward Arthur. Because when your whole existence is a lie, how can you trust even yourself?