One Dark Throne, by Kendare Blake, was published in 2017 by HarperTeen. It is the sequel to Three Dark Crowns.
With the unforgettable events of the Quickening behind them and the Ascension Year underway, all bets are off. Katharine, once the weak and feeble sister, is stronger than ever before. Arsinoe, after discovering the truth about her powers, needs to figure out how to make her secret talent work in her favor without anyone finding out. And Mirabella, the elemental sister thought to be the certain Queen Crowned, faces attacks that put those around her in danger she can’t seem to prevent….Fennbirn’s deadliest queens must confront the one thing standing in their way of the crown: each other.