Death By Fire by S.C. Muir

Marauding insurgents. An innocent life. Married strangers.

Fire and Water, Life and Death. The four types of magic held in perfect balance by the magi who wield them. That harmony shattered when a sorcerer wielding two opposing magics laid waste to the four clans, driving them into isolation.
Now, millennia later, leaders are trying to unite the clans once again. Mari, a Death Mage, is married off to a Fire Prince, Zahir, halfway across the world. Met with outrage and disarray, the pair must learn to navigate a marriage to a stranger and adjust to their sudden rise to King and Queen.

When their coronation is disrupted by violent insurgents, Mari and Zahir discover a horrifying truth: there is someone alive who can wield two types of magic once again. In a race against the clock, they must find the Dual Mage before the insurgents do, else an innocent person will lose their life.