The 52-year-old filmmaker has promised to expose the intimate details behind their break-up and has claimed the Hollywood duo were estranged for more than a year before their split in September 2016.
A source said: “This is the definitive film about Brangelina and a lot of secrets are going to come out.
“Ian has covered every cough and spit of their relationship and will reveal the real reasons behind Angelina filing for divorce.
“The biggest shock will be his claim that the couple were apart for more than a year prior to their break-up.”
Brad, 53, and Angelina , 41, are currently in the midst of a high-profile divorce and the documentary has been described as “the last thing they need”.
The source told The Sun newspaper: “[Ian] and his team have also managed to acquire some never-before-seen footage and interviews with both Brad and Angelina.
“Lately the pair have been trying to put on a united front and keep their divorce discussions quiet.
“This is the last thing they need.” Read More Here