The Turn Inside The Siren's Covenant

The Siren's Covenant keeps its sharpest change close to the facts the synopsis already gives you.

Before her death, she gives a final command: her newborn baby girl shall be raised as a boy under the name Elias Cole, and her true identity as a princess must be kept hidden. After the kingdom of Navia suffers defeat, the cowardly King Arthur Carter sacrifices women from his own realm to the invader Jaxson Kane in order to save himself and secure his throne.

Unable to bear the incoming humiliation, Queen Sophia poisons herself shortly after giving birth. Before her death, she gives a final command: her newborn baby girl shall be raised as a boy under the name Elias Cole, and her true identity as a princess must be kept hidden.

That is the spine of The Siren's Covenant: the people in the synopsis do not get to pretend the story started somewhere else.