Theirs is one of the most famous feuds in Hollywood history.

Now Angelina Jolie and Jennifer Aniston are to do battle once again – this time at the box office.

In a supremely ironic twist even by Tinseltown’s standards, Brad Pitt’s current romantic partner Jolie and ex-wife Aniston will go head to head at cinema theatres in mid-October, when both have a film coming out.

It's war: Angelina Jolie's film Changeling comes out the same day as Jennifer Aniston's He's Just Not That Into You

Jolie, who is pregnant with Pitt’s twins, stars in Clint Eastwood's missing-child drama Changeling; while Aniston is part of the ensemble cast in the romantic comedy He's Just Not That Into You.

Not surprisingly, insiders close to the pair confirm the contest is enormously personal to both actresses.

A source close to Aniston, 39, tells Mail Online: ‘The grudge Jen has against Angelina is so personal, failure just isn't an option.

‘Jen was happy to see Angelina’s last film, A Mighty Heart, fail at the box office, because she still thinks that role belonged to her, not Angelina.

Changeling: Angelina Jolie stars alongside Jeffrey Donovan in the Clint Eastwood-directed movie

‘She hates Angelina with a passion and won’t even utter her name.

‘Yes, she’s moved on with her life and has finally found a guy to settle down with in John Mayer.

‘But the bottom line is that Angelina humiliated her and as far as Jen’s concerned, made her an international laughing stock. She’ll never forgive her.

‘By winning at the box office with her next movie, Jen would achieve a small amount of much-needed closure.’

If pundits’ predictions prove accurate, Aniston stands every chance of achieving her goal.

He's Just Not That Into You: Jennifer Aniston stars in the ensemble romantic comedy, alongside Scarlett Johansson, Ben Affleck, Jennifer Connelly and Drew Barrymore

Most critics forecast that she stands the better chance of success because her film is receiving more promotion in the U.S.

But regardless of the final dollar figures, pride appears to be the biggest motivation.

‘For Jen, the logic is simple,’ the source observes.

‘Will people want to see a sexy and fun romantic comedy or two long, dreary hours of Angelina weeping over her missing child?

‘Jen makes these kind of movies to speak to her fans, and Angelina makes hers to try to win awards. Right now, there's no question in Jen's mind that her movie is going to crush Angelina's at the box office. She's welcoming the fight.’

The friend continues: ‘Jen has a real shot here to show Angelina - and the world - who the bigger star is.

Expanding their brood: Pregnant Angelina Jolie with Brad Pitt at the Cannes Film Festival last month

‘Jen can’t stand Angelina's holier-than-thou attitude and all the positive press she gets for her glamorous look and relationship with Brad. Beating her at her own game is a chance to make a real statement.’

Meanwhile the ever-confident Jolie is optimistic of box office success against her well documented nemesis, according to sources close to her.

A confidant told Mail Online: ‘It’s not even a contest to Angelina. She's always said Jennifer Aniston does frivolous, pointless movies and there's just no respect, on any level, for her acting ability.'

Aniston’s film, ‘He's Just Not That into You,’ is based on a lighthearted, best-selling relationship book endorsed by Oprah Winfrey.

The ensemble film has an all-star cast that includes Ben Affleck, Scarlett Johansson and Drew Barrymore.

But as audiences who have seen the coming attraction in front of the "Sex and the City" film already know, the movie is being sold largely on the back of its biggest name - Aniston - a star known for her impeccable instincts when it comes to the ‘rom-com’ genre.

Jolie’s Oscar-tipped effort, ‘Changeling,’ is a sombre and harrowing period film about a child abduction case in pre-WWII Los Angeles that won wide acclaim at the Cannes Film Festival last month.

Toyboy: Jennifer Aniston and her new boyfriend John Mayer