London, Aug 23 : American author Stephanie Meyer's Twilight series, which gives a glimpse of shadowy world of vampires, is proving to be a real threat to JK Rowling's Harry Potter.
Meyer's last book pushed down Rowling's 'Harry Potter and the Deathly Hallows' from the number one position of the best-seller list in the US.
And now the film based on Meyer's novel- with Kristen Stewart in lead- has delayed the release of 'Harry Potter and the Half-Blood Prince'.
The new Potter was expected to be released in November 2008, but now it has been shifted to July 2009.
The series of fantasy novel 'Twilight' features Bella Swan, an 18-year-old school girl, who moves to the sleepy town of Forks, Washington State, to live with her father and becomes drawn to Edward Cullen, her classmate, only to discover he and his family are vampires.
The pair then embarks on an unorthodox romance and battles the forces of evil.
The Twilight series has sold nearly 14 million copies worldwide with 10 million in US alone.
Twilight's fourth instalment, published last month has over 100 Internet fansites devoted to the books, Twilight-themed rock bands and clothing. Fans refer to themselves as 'Twilighters'.
A spokesman for Meyer's UK publisher, Little, Brown and co. said the word-of-mouth had turned the novels into a hit
"The first book had no marketing attached to it so we had few expectations. We have been taken aback by how fast the books have jumped up the best-seller lists," Telegraph quoted the publisher, as saying.