"Harry Potter and the Prisoner of Azkaban" marked a major turning point for the franchise when it hit theaters 15 years ago. Not only did it bring a new visionary director and newfound level of critical acclaim, it also transformed the series from a whimsical, family-friendly story of child wizards to a darker story about a young man confronting his terrible destiny. So celebrate this big milestone by learning more about the making of the third movie in the Harry Potter series.

1. After Chris Columbus declined to direct a third Harry Potter movie, WB pursued a number of potential replacements before settling on Alfonso Cuarón. That lineup included M. Night Shyamalan, Guillermo del Toro, Marc Forster, Callie Khouri and even series veteran Kenneth Branagh.

2. "The Prisoner of Azakaban" greatly expanded the scope of Hogwarts and the number of castle landmarks seen on-screen. Creator J.K. Rowling gave Cuarón a certain amount of freedom in that regard, but she did veto the idea of adding a graveyard, as she feared it would spoil upcoming books in the series.

3.Ian McKellen was offered the role of Albus Dumbledore following Richard Harris' death. He turned it down, not wanting to be faced with the pressure of bringing a second iconic wizard character to life.

4.Peter O'Toole was another major contender for the Dumbledore role, though concerns about his age and the cost of insuring the role caused the studio to look elsewhere.

5.Michael Gambon eventually won the Dumbledore part, despite the fact that he had never read the books and purposely avoided reading them for the remainder of the series.

6. The rival seeker who battles Harry for possession of the Golden Snitch during the Quidditch match is actually Cedric Diggory. Cedric is played by Joe Livermore in "The Prisoner of Azkaban," but the part was recast when Cedric took on a much more prominent role in "The Goblet of Fire."

7. The Honeydukes set is a modified version of the same set used for Olivander's wand shop in "The Sorcerer's Stone" and Flourish & Blotts in "The Chamber of Secrets."

8. Dudley Dursley actor Harry Melling was nearly replaced after losing a significant amount of weight in between the second and third films. Instead, Melling was given a fat suit for "Prisoner of Azkaban."

9. "The Prisoner of Azkaban" is unusual in the series in that it features several shots of practical illusionist tricks. Illusionist Paul Kieve was hired to serve as a consultant for the film and coached several of the actors.

10. "The Prisoner of Azakaban" is the final film in the series with a score composed by John Williams.

11. It's also the final film in the series to be released on VHS.

12. WB maintained strict secrecy surrounding the project, including referring to it by the codename "Radiator Blues" during post-production and providing night vision goggles to movie theater ushers to help combat digital piracy.

13. Despite being one of the most critically acclaimed entries in the Harry Potter series, "The Prisoner of Azkaban" is also the lowest-grossing of the eight. Huh.