Her King by Jade Marshall

The prophecy was only the beginning. The crown was never the end.

After surviving betrayal, bloodshed, and a bond forged in fire, Cassandra has become the key to peace—or annihilation. Her soul now bears the mark of three realms: Earth, Runic, and Quietus. And not everyone believes a witch should hold that much power.
As war erupts and shadows rise, Cassandra and Niko must navigate deadly court politics, ancient magik, and enemies hidden in plain sight. With a traitor in the palace and the prophecy unravelling around them, the couple must decide how much are they willing to sacrifice for a peace the realms may not deserve?

Love gave them strength.
War will decide their fate.
And only one truth remains:

To save the realms, she must become their queen. Even if it means breaking everything.