Family of the Solstice: Book 1 - The Moon and Its Eclipse
Before their mother's passing, she granted the title of Duchess of Draya to Vexeon. She made Vex promise her two things, to protect the kingdom of Vaicuria and most of all, to protect Lunette. For there is a secret that only they know about Lunette, which can put her in danger and even start an epidemic of violence.