Harry Potter and the Order of the Phoenix is the longest book in the series at 766 pages in the UK version and 870 pages in the US version, yet it is the second shortest film at 2 hours and 18 minutes.

Unlike the previous seven books, the eighth book was originally, and actually, a play titled "Harry Potter and the Cursed Child" that debuted on the 30th of July 2016 (on Harry's birthday).

Fortunately, however, J.K. Rowling, the author of the Harry Potter series, announced that the script of the play will, in fact, be released as a two-part book, at 12:01 a.m. back on July 30, 2016.

More Info: en.wikipedia.org