Angelina Jolie, pictured with Shiloh, Zahara and Maddox, is 'constantly tired from taking her four kids to Texas where Brad is filming

"We are legally bound to our children, not to each other, and I think that's the most important thing."

The actress is pregnant with twins - reported to be a boy and a girl - and is due to give birth later this year.

The pair already have three adopted children, Maddox, Zahara, Pax-Thien, and a biological daughter, Shiloh.

Angelina was previously married to British actor Jonny Lee Miller and Billy Bob Thornton while Brad split from his wife Jennifer Aniston in 2005.