Chaste Blood: Repressed Royals, Book 1 (Unabridged‪)‬

Kill your mate. Live forever. 

As the only princess in the Shadow Court, Sinna has lived a painfully sheltered life. She knows her dream of becoming a ruthless Hunter—those charged with killing the fated mates of anyone in her court—will never be more than just a dream. An opportunity arises when her own mate is revealed to be the King of the Blood Court. Now Sinna's only hope of proving herself is to infiltrate the enemy court, seduce, and slay the Vampire King, and hope that her immortality holds out longer than his. Failure will not only mean a painful bloodless death for her but bring ruin to her entire court. 

King Maddox of the Blood Court knows a liar when he meets one, but anything would be better than the mundane eternal existence he's endured thus far. When a stranger enters his court and challenges his restraint, he's eager to test his limits—and hers. But darker forces seek to make pawns of both preoccupied royals. Let the battle of wills commence.