Is Brad Pitt and Angelina Jolie’s union on the rocks? Are they truly compatible? Author Ian Halperin talks about America’s most fascinating couple in his new book, Brangelina: The Untold Story of Brad Pitt and Angelina Jolie to ET… In the book, available starting today, investigative journalist Halperin promises to expose “what’s true, what’s not, and what really has gone on behind closed doors with [Brad and Angelina].” Halperin tells ET, “Angelina and Brad are deeply concerned about the …