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Their passion was evident and often on display on the red carpet. But for some time, it was believed that Angelina Jolie’s decision to adopt Maddox was behind her and Billy Bob’s marriage coming to a halt.

Now, Billy Bob is opening up about the real reason they split, and it seems that his personal insecurities were the root of the problem.

In an openly frank interview with ABC’s Nightline, he admitted: “I blew it because I didn’t think I was good enough for her. She has one way she wanted to live her life and I had another way to live mine and I was just too insecure.”

“I did feel like the Phantom of the Opera hiding in the catacombs,” he added. “People have actually said that I didn’t deserve to be with her.”

He also goes on to explain that her rising fame was also a factor. When they first married in 2000, he was the more famous of the two, but by 2001, she had begun her rise to mega-stardom for her portrayal of video game heroine Lara Croft in “Lara Croft: Tomb Raider”.

“When you’re in a relationship, any two celebrities or whatever, you know, I think that puts on a lot of pressure,” Thornton said. “When Angie and I got married, during that time, I was more famous than she was to start with and then when she becomes this big thing, it’s hard in these relationships.”

He also cleared up some misconceptions about the pair, who were married for three years, namely those blood vials they wore around their necks.

“[Jolie] bought these clear lockets, they were little bitty things,” he said. “Angie and I literally poked each other in the finger with a pin and rubbed a little bit of it on that locket. When we were apart, it was a symbolic thing to do.”

Nine years on since the end of their marriage, Billy Bob says he and Jolie remain “good friends”.

“We had a great time together,” he said. “We had a great marriage and I chickened out because I didn’t feel good enough. That’s all that happened. It was no big deal, we never hated each other.”

As testament to their enduring friendship, Jolie even penned the forward to her ex-husband’s book, in which she writes about Thornton’s quirks and funny times they shared together.  At one point, Jolie calls him the “mad mathematician” and writes, “To him, I am the number four. May sound strange, but it means a lot to me.”

When asked what “number four” refers to, Thornton said, “That’s something that no one will ever know.”

What do you think number four refers to? Let us know….

“The Billy Bob Tapes: A Cave Full of Ghosts” will be in stores on May 15.