A number of pictures have turned up online today showing that filming has begun on The Hangover 2, the sequel to 2009’s sleeper comedy hit.

The four lead actors – Ed Helms, Bradley Cooper, Justin Bartha and Zach Galifianakis – were caught on camera in Ontario, Canada filming an airport scene. It puts to bed speculation that Bartha would not be reprising his role as Doug Billings for the sequel.

Despite details being kept under wraps, The Hangover 2 supposedly takes place after a hard night of partying, when Stu (Helms) gets really drunk and ends up sleeping with a Thai tranny. The next day the guys have to try and rehash the night and figure out what happened.

The Hangover 2 was written by Scot Armstrong and is being directed by Todd Phillips. The film is likely to be release during the latter half of 2011.

Check out two pictures below, or head over to PopSugar for the whole foray: