Haven't read this series as it's currently unfinished (There are five planned, of which four is due next month) but I have read The Night Angel Trilogy by the same author, and that was a cracking read.
EVERY LIGHT CASTS A SHADOW
Gavin Guile is the Prism, the most powerful man in the world. His strength, wit and charm are all that preserve a tenuous peace. But Prisms never last, and Guile knows exactly how long he has left to live.
When Guile discovers he has a son, born in a far kingdom after the war that put him in power, he must decide how much he's willing to pay to protect a secret that could tear his world apart.