Is Angie the worst Mean Girl of them all -- and is Brad's ex-wife Jen her most-wounded victim?

Brangelina: The Untold Story of Brad Pitt and Angelina Jolie reports that Angelina Jolie, 34, waged "a mean-spirited but effective campaign" against Jennifer Aniston around the time that Brad Pitt divorced her to be with Jolie.

The new Us Weekly (on newsstands now) has the exclusive first look at what's really inside the shocking new tell-all -- and reveals the truth behind some of the alleged bombshells.

Author Ian Halperin asserts in his book that Jolie and her camp (including her manager Geyer Kosinski and brother James Haven) planted press stories in 2005 that painted Aniston in a negative light. Specifically? That Aniston firmly prioritized her career over starting a family -- which put her directly at odds with Pitt, who ached for kids.

Jolie, Halperin writes, "was convinced that this is the story that would resonate with all these women who saw her as a man-stealing bitch."

For more on Jolie, Pitt and Aniston - including the truth behind Jolie and Pitt's supposed infidelity, their absentee parenting, and Jolie's "warning" to lookalike Megan Fox - pick up the new issue of Us Weekly today!