Brad Pitt and Angelina Jolie have decided six children is not enough, if recent reports are to be believed.

Star magazine in the US claims Jolie is pregnant with another child, more than four years after the actress gave birth to twins Knox and Vivienne.

The couple are also already parents to Maddox, Pax, Zahara and Shiloh.

"Angelina has been talking about having another child for years now. But Brad kept putting his foot down because of their intense schedules and chaotic lifestyle," the magazine quotes a source as saying.

But it looks like Pitt may have lost that argument with rumours Jolie is pregnant with another son.

The magazine's source says the mum of six is keeping a low profile to hide her pregnancy.

"She had morning sickness and didn't want to draw attention to herself in public," they said.