Legacy of Light (The Legacy Trilogy, #3) by Matthew Ward

Legacy of Light is the spectacular conclusion to Matthew Ward's acclaimed Legacy trilogy—an unmissable epic fantasy series of war and intrigue perfect for fans of George R. R. Martin, Brent Weeks, and Brandon Sanderson. 
 
For the first time in many years, the Tressian Republic and the Hadari Empire are at peace. But darkness never sleeps. 

In Tregard, Empress Melanna Saranal struggles to protect a throne won at great cost. 

In Tressia, Lord Protector Viktor Droshna seeks to restore all he's lost through forbidden means.

And as the sins of the past are once more laid bare, every road will lead to war.

 
The Legacy Trilogy
Legacy of Ash
Legacy of Steel
Legacy of Light