The Hangover was a hit in 2009 first and foremost because of its cast - Ed Helms, Bradley Cooper, and Zach Galifianakis have an undeniable chemistry - but, according to The Hollywood Reporter's "Uncensored Oral History of The Hangover," that could have all been different.

Though Helms was cast from the get-go, both Paul Rudd and Jack Black turned down roles in the project before production was set to begin - and, originally, Galifianakis's character, Alan, was a completely different character. As director Todd Phillips explained:

When we were writing, we did have [other actors] in mind. Quite honestly, we were writing the brother-in-law as a younger brother they had to take along with them -- like a Jonah Hill character instead of Zach [Jake Gyllenhaal also was considered]. Then we thought it'd be so much more awkward if it was an older brother who's still at home. [Thomas Haden Church was strongly considered.] I've always been a huge fan of Zach [as a comedian and actor], but Zach didn't want to come out and meet with me.

The more you know!

The third sequel to The Hangover franchise is set to hit theaters on May 24th. 

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[via The Hollywood Reporter]