J.K. Rowling always said that Harry Potter and the Deathly Hallows would be the last book in the Harry Potter series, but if 2016 taught us anything, it's that Rowling is more invested in the wizarding world than ever. In the years since The Deathly Hallows 's release on July 21, 2007, Harry Potter has become Rowling's Room of Requirement: Sometimes it's there, and sometimes it's not, but when it does appear, it becomes whatever she needs it to be.