How many underworld books are there?

there's altogether four novelizations in the underworld novel series, three of then are novelizations to the films such as Underworld, Underworld: Evolution and Underworld: Rise O f The Lycans, the fourth novel is Underworld: Blood Enemy, which isn't completely tided to any of the other stories, the fourth is more or so a fan fiction base novel, the blood enemy story is a prequel, but it's not told the same way as it is in rise of the lycans, also in blood enemy, it gos back and fourth to the dark ages and to the modern day and in the modern day scences are what happens a few days or weeks before the events of the story of the first novel of underworld take place in, but most of all, it's the other three novels that are the main underworld stories