Claim: Justin Bartha is in The hangover Part III.

The Hangover Part III is a 2013 American comedy film produced by Legendary Pictures and distributed by Warner Bros. . Pictures . It is the third and final installment in The Hangover trilogy . The film stars Bradley Cooper , Ed Helms , Zach Galifianakis , Justin Bartha , and Ken Jeong . The supporting cast includes Jeffrey Tambor , Heather Graham , Mike Epps , Melissa McCarthy and John Goodman with Todd Phillips directing a screenplay written by himself and Craig Mazin . The film follows the `` Wolfpack '' -LRB- Phil , Stu , Doug , and Alan -RRB- as they try to get Alan the help he needs after facing a personal crisis . However , things go awry when an incident from the original film comes back to haunt them .   The Hangover Part III was announced days before the release of The Hangover Part II and Mazin , who co-wrote Part II , was brought on board . In January 2012 , the principal actors re-signed to star . In March 2012 , Warner Bros. announced a U.S. Memorial Weekend release . The supporting roles were cast between June and September 2012 . Principal photography began in September 2012 in Los Angeles , California before moving to Nogales , Arizona and Las Vegas , Nevada . The film was released on May 23 , 2013 .