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Newly-engaged Angelina Jolie has poured her heart out about ex-husband Billy Bob Thornton in the foreword of his memoirs.

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The actress split from the Oscar winner a decade ago, but it is clear she still has feelings for her former partner as she plans to wed Brad Pitt.

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Cooing about the actor in the foreword of his new book The Billy Bob Tapes: A Cave Full of Ghosts, Jolie writes, "[Thornton] has an unmatchable wit and can make you laugh until your face hurts," adding that the star "has a big beautiful heart."

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Jolie will never forget how clever her eccentric ex-husband is: "To be with him is like being with a mad mathematician. He is constantly counting and repeating."

The actress concludes with a touching tribute to Thornton, adding, "Some people walk through life able to quiet the voices in their heads. He can't. And I, and everyone else who knows him well, we love him for it. I know one thing: The world would certainly be a hell of a lot more dull if that man weren't in it."