Brad Pitt and Angelina Jolie's united front at Cannes ended the moment they were out of sight of the cameras, according to eyewitness reports.

The pair were all smiles and loving looks as they hung off each on the red carpet at the premiere of Brad's new movie Inglourious Basterds during the film festival.

But rumours persist that their public displays of affection mask a seriously rough patch in their four-year relationship.

Onlookers reportedly said the end of the couple's Cannes love-in was signalled by a furious Angelina fleeing from the theatre with Brad running after her.

All an act? Angelina and Brad share an awkward moment on the red carpet in Cannes

A major source of conflict is said to be Brad's increasingly close relationship with ex-wife Jennifer Aniston.

It's alleged that Angelina initially refused refused to travel to France to support Brad  unless he cut off all contact with the Marley & Me star.

"Angie doesn't want to be a laughing stock because the world knows how close he and Jen are right now and how often they talk," a source tells Britain's Grazia magazine. "

But Brad wants to remain friends with Jennifer and told Angie he wouldn't cut off contact."

Meanwhile, the couple are unlikely to be spending much time in each other's company in the near future – Brad is about to embark on an international promotional tour for Inglourious Basterds, whilst on Monday Angelina was back on the New York set of her upcoming spy thriller Salt.

See more of Angelina & Brad in Cannes below