Pitt, 50, who has six children with his 'Maleficent' star wife, is believed to have lost more than 10 pounds after participating in the intense military-style exercise classes for just three weeks and is even letting his kids join in the fun, reported the Daily Mirror.
"The whole family are learning the moves, even the little ones are doing modified kids' moves but Brad has been doing it for 45 minutes a day and has dramatically lost weight and beefed up his muscles for the film," a source said.
'By The Sea' has been written and directed by Jolie and will mark the first time the newlyweds have starred together on screen since they met on the set of 'Mr and Mrs Smith' in 2005.