Jolie, who divorced Thornton in 2003, has written the foreword for her ex-husband's upcoming memoir, The Billy Bob Tapes: A Cave Full of Ghosts, due out May 15.
Jolie isn't the only famous person who contributed. An image of the cover of Thornton's book posted on Amazon reads, "Introduction by Angelina Jolie, with commentary by Robert Duvall, Dwight Yoakam and Tom Epperson."
A description of the book posted on the site says The Billy Bob Tapes will include "colorful tales of his modest (to say the least) Southern upbringing, his bizarre phobias (komodo dragons?), his life, his loves (including his heartbreakingly brief marriage to fellow Oscar winner Angelina Jolie), and, of course, his movie career."
"I thought she did an amazing job," he said. "She really dug deep and it meant a lot to her. I'm very, very proud of her."
Jolie was also at the Berlin Film Festival where she was given a standing ovation after she screened her directorial debut.