What happens when a group of celebrated actors read a script live, on-stage for the very first time? Pure magic? Inconceivable! But that's exactly what happened last night during Jason Reitman's live-read of The Princess Bride, a cult-classic that originally screened at TIFF in 1987.

Thousands packed into the Ryerson Theatre yesterday to hear the movie's screen-play read aloud by an all-star cast that had neither met, nor rehearsed prior to the show. As Reitman introduced the performance, he promised we'd get to see the actors "find it" as they progressed through the show.

Earlier in the week, Reitman disclosed certain casting choices via Twitter including Donald Glover as Vizzini, former NHL-er Georges Laraque as Fessik, a role originated by Andre the Giant. He revealed local actress Rachel McAdams as Princess Buttercup, Gage Munroe as the grandson, Chris O'Dowd as Count Rugen and Gael Garcia Bernal as Spanish swordsman Inigo Montoya.

This left room for numerous surprises, and the crowd went nuts when Reitman brought legend Patrick Stewart to be Prince Humperdinck - he played the villainous royal with glee.

The Princess Bride director Rob Reiner rounded out the cast as the grandfather. With one hole left, Reitman announced Cary Elwes as Westley; yes the British actor reprised his 1987 role.

Reitman read the stage directions and being live theatre, actors fudged their lines - Bernal nearly missed the entire performance thanks to a delayed flight. Meanwhile, Reitman's sister Catherine filled in, garnering huge laughs for her rendition of, "Hello. My name is Inigo Montoya. You killed my father. Prepare to die."

At one point, Elwes whipped out his phone to take of photo of Stewart who was sitting beside him. And the cast burst into laughter and applause as they delivered line after memorable line, clearly enjoying the performance as much as the audience.

O'Dowd, in town for the Lance Armstrong biopic The Program, seemed to have the most fun putting on ridiculous voices as he played the evil count as well as Miracle Max. McAdams hilariously jumped in as his wife Valerie.

Laroque was an impressive Fessik and Reiner led the audience through the story along with Munroe. When Reiner delivered the final "as you wish," the crowd leapt to its feet, almost begging him to read the story again.

Photo via TIFF on Instagram.