Immortal Sentry by Eden Winters

Honor, redemption, destiny, and magic.
As captain of the king’s guard, Kerric should have laid down his life for the royal family. Now, the king and his heirs lie dead. Kerric deserves death, too, yet the court mage has another punishment in mind. For their failure on the fateful day an enemy invasion killed the king, Captain Kerric and his men will forever guard the castle as gargoyles, both as a curse and as a warning. His one chance for redemption is to put a rightful heir on the throne. How can that happen when there are no living heirs, and he’s encased in stone?
Eron doesn’t remember much about his time before being rescued by notorious highwayman Lord Night and taught to live the life of a noble by day and brigand by night. There’s much more to Lord Night than meets the eye and much more to Eron’s destiny than purses of gold and nightly conquests.
A mysterious mage appears, saying it’s time for Eron to return home, overthrow an evil usurper, and take his rightful place.
As king.