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Author Sara Shepard will add four new books to her Pretty Little Liars series, starting with a July 2011 release, EW has learned exclusively. The new books — from Alloy Entertainment and HarperCollins — will bring the total in the series to 12. Though the number was originally capped at eight, the ABC Family show based on the young-adult mystery series — which follows the aftermath of a popular girl’s disappearance — has been a ratings success and renewed interest in the books. The first new installment, Twisted, will be on sale July 5; Shepard’s The Lying Game was just released.