Jane Pitt believes "manipulative" Angelina is to blame for Brad's emotional turmoil.
"Jane is a tough cookie, and she will never forgive Angelina for what she’s put the family through – especially since they’ve barely seen the kids since the divorce was announced," a source told Radar Online.
"She thinks her son has been treated in a cruel and manipulative way, and she’s not letting this go."
"Brad’s had to beg his mum not to jump on a plane to confront Angie numerous times, but she wants to look her in the eye and give a piece of her mind," said the insider.
"She blames her for her ruining her son’s life and wants answers."
Last November, Pitt and Jolie finally reached a custody agreement over their kids, Maddox, 17, Pax, 15, Zahara, 13, Shiloh, 12, and 10-year-old twins Vivienne and Knox.
"A custody agreement was agreed to weeks ago, and has been signed by both parties and the judge," Jolie’s lawyer, Samantha Bley DeJean, told Entertainment Tonight.
"The agreement, which is based on the recommendations of the child custody evaluator, eliminates the need for a trial.The filing and the details of the agreement are confidential to protect the best interests of the children."