The Medici Guardians – Book 5: The Last Judgment. The Medici Guardians, #5

Aria thought she understood the weight of the violet seal. She was wrong. Three weeks after Vittoria's warning, Aria and her four guardians-Marco, Enzo, Luca, and Dante-drive to Rome under the cover of darkness. Their destination: an ancient villa on the Appian Way, hiding a crypt that has waited five centuries for this night. Beneath the ruins sleeps Cassia. The mother of mothers. The first queen.
The one who wore the double seal before Isabella, before Livia, before Aria. She is not a monster. She is something far more dangerous: a judge who grew tired of judging. To earn Cassia's wisdom and free the forgotten queens scattered across Italy, Aria must pass three tests. The test of truth, where mirrors reveal the women she might become. The test of blood, where memory becomes currency. And the test of the heart, where she must choose who will carry the violet forward.
But Cassia harbors a secret deeper than any curse. And when the final judgment comes, Aria will learn that the violet seal was never meant to be carried alone. The Last Judgment is the fifth book in the Medici Guardians series.