Bradley Cooper immediately called Zach Galifianakis after his dad died.
The 'Hangover Part III' hunk has formed a close bond with his co-star after working on three films together, and he leaned heavily on his pal following his father's death in January 2011.
He told Italy's A magazine: ''Zach is one of my best friends; he's the one I go to when something's wrong. He is the first person I called when my father died.''
The actor also insists fans relate to the 'Hangover' movies because the cast - which also includes Ed Helms, Ken Jeong and Justin Bartha - play ''real men'' who have emotional baggage.
He explained: ''I think the reason why everybody likes our characters in 'Hangover' is because we portray real men. We can mess things up, but eventually we all need real friendships.''
Bradley previously credited the franchise's success to the characters to the friendship between the three lead characters.
He said: ''The chemistry between the three of us is the main reason for it, I think. It's kind of every man's fantasy to have amazing friends with whom you can live it up at the age of 20, and still do the same when you're pushing 40.
''I think a lot of people see a bit of themselves in Phil, Stu and Alan.''
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