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"I wrote something a few years ago for Brad and me. Just for fun," the Oscar-winning actress says in the latest issue of People.
"Just an independent little art piece. Because we don't get to do those as much as we'd like. But it's something really small and experimental."
Jolie also dishes on her wedding plans, revealing she's getting plenty of input from the couple's six kids: Maddox Jolie-Pitt, 12, Pax Jolie-Pitt, 10, Zahara Jolie-Pitt, 9, Shiloh Jolie-Pitt, 7, and twins Knox Jolie-Pitt and Vivienne Jolie-Pitt, 5.