“She hired a private eye because she felt that he was fooling around with her on the set, and it turns out, he was. And that was the final straw,” the source said.
Pitt, 52, had been rumored to have been cozying up to his “Allied’’ co-star Marion Cotillard, 40, for months during the pair’s filming of the World War II drama in London.
The PI discovered that was Pitt cheating on his wife of two years with Cotillard — while also partying like a single guy on a mission, the source said.
“The atmosphere [off-set] was full of hard drugs and Russian hookers, and Angie was told Brad got caught up in it,” the source said.
“He’s in the throes of some insane midlife crisis, and Angie is fed up.”
Jolie, 41, was sick and tired of sparring over their lifestyle, another source said.
She has increasingly wanted to quit Hollywood in favor of devoting herself full-time to traveling the globe for her humanitarian work, while Pitt prefers Tinseltown and its parties, the source said.