Prince of Blood by Ana Calin

Dracula exists.
For centuries he’s been lurking in the underworld, searching for the one woman whose blood can make him invincible–Dracula’s Grail.
A shadow stalks librarian Ruxandra Len, a demonic power from a past she can’t remember. Intrigued when she discovers that her bloodline leads back to the notorious Prince Dracula, she travels to the Carpathians to learn more. But what she finds is a truth darker than legend.
The Prince of Blood fascinates Rux. His dark energy weaves a web of enchantment around her, making her crave him. But just as the Dark Lord thinks she’s ready to surrender her blood, the deepest shadow of her past emerges. Can Vlad Dracula defeat an even older, darker legend, and protect the woman who means the world to him in more ways than he likes to admit?