The Young Queens by Kendare Blake

Three black witches, born to a descending queen. One would rise to become queen in her place. Perhaps the strongest of the three. Perhaps the cleverest. Or perhaps it would be the girl born under the best shield of luck.
Katharine, Arsinoe and Mirabella - three young queens born to fulfil their destiny - to fight to the death to win the crown. But before they were poisoner, elemental and naturalist, they were children, sisters and friends . . . Discover the origin story of the three queens of Fennbirn in this exclusive e-novella from Kendare Blake, bestselling author of the New York Times bestselling, Three Dark Crowns.
What everyone is saying about Three Dark Crowns:
'A brutal and inventive fantasy that is as addictive as it is horrifying.' Marissa Meyer, NYT bestselling author of The Lunar Chronicles on Three Dark Crowns
'Gorgeous and bloody, tender and violent, elegant, precise, and passionate; above all, completely addicting.' Kirkus Reviews on Three Dark Crowns