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Shia LaBeouf says he trained intensely for two months and gained a whopping 50 pounds to prepare for his role in the prohibition-era gangster film Lawless.

LaBeouf told ET at a screening of the movie last night in New York that he was pushed hard by co-stars Tom Hardy and Jason Clarke -- who play his siblings in the film -- to "train harder than anybody who showed up for this film."

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"There's a fabric of the family that needs to exist, he explained. "So had I showed up in my fighting weight -- which is 130 -- next to Hardy I wouldn't have looked like I was related. So I shipped out at 180 and he dropped his weight. And Jason upped his weight and we all tried to level out."

Lawless -- also starring Gary Oldman, Guy Pearce, Jessica Chastain,  Mia Wasikowska and Dane DeHaan -- tells the story of the bootlegging Bondurant brothers in Depression-era Virginia. The government tries to persuade the brothers -- played by LaBeouf, Hardy and Clarke -- to give them a share of their profits in exchange for immunity from arrest.

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Chastain revealed there was plenty of "masculine energy" on the set that she didn't mind, but one day she admits she was glad to see another actress show up. "After a few weeks of filming, as much as I love the guys, the first day Mia Wasikowska was there, I ran into the makeup trailer and I threw my arms in the air and I just yelled out, 'It's a girl!' I was so happy."

Watch the video to hear DeHaan talk about how it was his "dream come true" to work with the talented cast of Lawless, which hits theaters August 29.

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