Prince of Twilight. Wings In the Night, #9

Strong sexual content Dracula is far older than his legend. For centuries, he has awaited the reincarnation of his one true love, Elisabeta, foretold by the vampire Rhiannon centuries ago. And now he has found her. But she has not returned to him in the way he expected. Instead, her restless and frustrated spirit is possessing a modern-day woman named Tempest, who is called "Storm." The nickname, he finds, is fitting. Stormy has been sensing a presence inside her fighting to take control.
That feeling becomes even more overwhelming when the dark prince is near. She is torn between her own passion for Vlad Dracul, and the passion of the entity lurking within. The parasitic and jealous Elisabeta wants to kill her hostess when she realizes they both love the same man. It's a fight to the death within a single body. But only Vlad can choose which of his loves will live and which will die.