By Mistake. Fools & Demons, #1

Andrus is a man in despair. His family, once illustrious and powerful, was destroyed forever when his great grandfather betrayed everyone and killed a beloved royal prince. Now the last of his bloodline, Andrus is mere days away from losing what little he has left, and his only options are living on the streets or surrendering himself to a man he despises. Oresti is a man of secrets and lies, his days spent as a city investigator dealing with the worst people in the kingdom, his nights fulfilling his duties as a royal prince and solving unsavory problems for his father.
Currently he is charged with determining whether the recent death of a powerful duke was truly natural, and if not, who is responsible for his death-and why they killed him. Desperate to escape the horrid fate awaiting him, Andrus attempts the very magic he's forbidden from using-but instead of the harmless helper he meant to summon, he instead calls forth one of the most dangerous demons in existence, setting off a chain of events that will drag mysteries old and new into the light, and save or destroy a kingdom.