Angelina Jolie and Brad Pitt to star together in an ''experiment.''

The couple - who became romantically involved after meeting on the set of 'Mr and Mrs Smith' in 2005 - are planning to collaborate on a movie penned by the 38-year-old actress - who insists the ''small'' and ''independent art piece'' will be a world away from the action blockbuster in which they met.

She told People magazine: ''I wrote something a few years ago for Brad and me. Just for fun.

''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.''

As well as appearing with her husband, the pair's five-year-old daughter Vivienne recently received her first acting credit, starring alongside her mother in 'Maleficent' as the young Princess Aurora.

However, Angelina - who also has Maddox, 12, Pax, 10, Zahara, nine, Shiloh, seven, and Vivienne's twin brother Knox with 50-year-old Brad -admitted she wasn't too keen on Vivienne appearing in the film.

She said: ''I don't want our kids to be actors. But we realised early on that four and five year olds were not going to be comfortable in a scene with me. I would say hello to kids and they would cry.

''So I went back and said, 'Maybe...' So Brad and I had a long talk about it because it wasn't an easy choice to kind of make her [Vivienne] more public. But we thought less of that and more of time spent on-set with Mommy.''