The third party in Bradley Cooper and Renee Zellweger's split revealed: His career

Speculation that another woman was the reason behind Bradley Cooper and Renee Zellweger's shock split are untrue, a friend of The Hangover star says.

Instead, the source has pointed to Bradley's rising career as the culprit.

'If I had to pick any possible mistress it would be Brad's career. He worked really hard to get into leading man status,' the friend says.

Happier times: Renee and Bradley dated for nearly two years but have now gone their separate ways

Split: Bradley Cooper and Renee Zellweger, pictured last year, split because of his career, according to sources

News that the couple had parted ways emerged last week, just days after 36-year-old Cooper paid tribute to Renee, 41, during a interview on biographical series Inside The Actor's Studio.

Cooper has seen his career rise stratospherically since starring in hit comedy The Hangover in 2009 after years in supporting roles in films such as Wedding Crashers and Failure To Launch.

Last weekend his first film as a leading man, Limitless, topped the US box office and took in $19 million.

Leading man: Bradley's career is on the rise and his first film as a leading man, Limitless, has just topped the US box office

Leading man: Bradley's career is on the rise and his first film as a leading man, Limitless (with Robert DeNiro), has just topped the US box office

Speaking to Us Weekly, the source added: 'Renee had to take a backseat. She travelled with him to make it work.'

'She's accomplished a lot of her professional goals. So Renee took some time out to be a great girlfriend and see if this is what it took to make a relationship work.'

Bridget Jones star Renee even moved from her New York base to Los Angeles to be closer to Bradley.

However, the source added; 'She stopped fighting. It was just not working out.'

Brave face: A solo Renee Zellweger dines alone at a restaurant in New York yesterday just days after her split from boyfriend Bradley Cooper

Brave face:  Renee Zellweger dined alone at a restaurant in New York on Sunday

Renee was back in New York this week, where she visited fellow singleton Sandra Bullock.

The Bridget Jones star was spotted arriving the Blind Side actress' apartment during a trip to New York over the weekend.

The 41-year-old's visit came just a day after she'd split from actor Bradley Cooper following almost two years together.

Of course, Sandra is no stranger to heartache having endured a very high-profile divorce from Jesse James last year following his string of infidelities.

Shoulder to cry on: Renee Zellweger visited her friend Sandra Bullock's NewYork home today for advice on dealing with a public break-up after her split from Bradley Cooper
Shoulder to cry on: Renee Zellweger visited her friend Sandra Bullock's NewYork home today for advice on dealing with a public break-up after her split from Bradley Cooper

Shoulder to cry on: Newly-single Renee visited Sandra Bullock's New York apartment last week

The two Oscar-winners were not known to be friends, however they do share a Texas connection. Renee is a native of the state The Blind Side star has a home in Austin.

The 41-year-old turned up to Sandra's West Village apartment in her usual gym attire that included grey three-quarter leggings and trainers.

Sandra is currently based in the city with her son Louis while she shoots her new movie, Extremely Loud and Incredibly Close.

Of course, there would have been no shortage of talking points for the pair, with Sandra now an expert in handling life in the spotlight after a break-up.

Jet-setting: Cooper is busy on the promotional trail for his new film

Jet-setting: Cooper is busy on the promotional trail for his new film

Renee appears to be bouncing back well after the split - She went to a friend's party at La Esquina restaurant on Saturday night and attended the premiere of Bette Middler's new Broadway musical Priscilla Queen of the Desert after a solo brunch at Le Pain Quotidien on Sunday.

A friend of Renee's told U.S. magazine: 'She tried to make it work, but in the end it was too hard. Her friends feel bad it ended, but she's okay'.

Renee has not had many major film projects in the last couple of years but a Bridget Jones 3 is said to be in the works.

Blockbuster: He will be back on screens in the highly-anticipated Tha Hangover: Part 2 later this year

Blockbuster: He will be back on screens in the highly-anticipated The Hangover: Part 2 later this year

A source close to the actress told People magazine that Renee is ready to focus on her career again after taking some time out from the big screen.

'She hasn't been working because she wanted to really put time and energy into the relationship and now she's going back to work', the insider added.

Cooper is currently promoting his new film, Limitless, which topped the U.S. box office over the weekend

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