Books like The Bone Doll's Twin by Lynn Flewelling

For three centuries the throne of Skala was guarded by a line of powerful warrior queens, bound by prophecy and magic. When usurper king Erius forces his claim upon the throne, famine, war with Plenimar, and the threat of a dark oracle spread across the realm. The king’s own blood becomes his greatest danger when the only male heir is a boy born of a royal half‑sister, while the survival of the royal line now depends on a princess transformed into a boy by dark magic. With the help of her noble father, two wizards of the kingdom of Illior, and a forbidden forest witch, the girl‑boy—known as Tobin—must evade the king’s cruel ambition, madness, and the vengeful demon spirit of her brother. The novel explores themes of destiny, gender and power, and the costs of war, all set against a richly imagined fantasy world where magic is both a blessing and a danger.

First publish date: 2001