The Princess Bride hit theaters in September 1987 and was a modest success at the box office. However, it has become a cult classic over the years, a family movie that keeps getting passed on. The comedic fantasy movie isn't just hilarious to audiences, according to a new interview with director Rob Reiner, who admits that Billy Crystal's ad-libbing on the set was too much for him to take. Reiner also revealed his favorite line from the very quotable film.

Billy Crystal is recognized as one of the best comedians to ever step foot on stage by many, including the late Robin Williams. Crystal and Williams were able to crack each other up with their intense ability to quickly ad-lib, which gave them both practice for their acts. When it came time to film The Princess Bride, Crystal was at the top of his game, which proved to be difficult for Rob Reiner on the set. The director explains.

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"Billy ad-libbed a lot while we were shooting and I started laughing. I'd laugh. I ruined five or six takes because you know when he says A mutton, lettuce, and tomato sandwich? I was gone."

It's not every day that you hear of a director ruining a scene while working on a movie from laughing too hard. It's usually the exact opposite, with the actors and actresses messing each other up. But Billy Crystal had that power over Rob Reiner, which probably resulted in a much longer day of filming for certain scenes. Reiner has worked with some of the best ad-libbers in the business, including Christopher Guest (who is also in The Princess Bride), Harry Shearer, and Michael McKean on 1984's This Is Spinal Tap.

Rob Reiner also shared a story about his favorite line from The Princess Bride, which is, "My name is Inigo Montoya. You killed my father, prepare to die." The line is very popular, and one has to imagine that Mandy Patinkin still hears that quote on a weekly basis. Reiner says that he was out at a restaurant one day when infamous mobster John Gotti walked in with his crew. As the director exited the restaurant, one of Gotti's henchman repeated the line to him and told him how much he loved the film, much to Reiner's surprise.

Rob Reiner has had an incredible career, starting with working as an actor on All in the Family to directing A Few Good Men. The director has created some of the most beloved movies in cinematic history, and The Princess Bride is right up there with his best, which also includes the romantic comedy When Harry Met Sally, a movie that starred his good buddy Billy Crystal. The director has not revealed if he ruined takes on that film because of Crystal's ad-libbing skills. You can check out the rest of the interview with Rob Reiner over at Entertainment Weekly.