Jennifer collapses on set

Jennifer Aniston has collapsed on the set of her new film as reports grow of a romance between her estranged husband Brad Pitt and Angelina Jolie.

The former Friends star fainted after complaining of nausea and headaches while filming The Break Up in Chicago.

Although the 36-year-old actress was officially diagnosed as having heatstroke, sources on set say she appears to have been badly affected by the increasing evidence that during her marriage to Pitt he was having an affair with Miss Jolie, 30. One source said: 'She's been walking around with a sad look on her face and has not been her usual self.

'In between takes she sat at her table with her head in her hands looking distressed.

'She has talked about how she is not sleeping well, although she has been trying to be as brave as possible.

'She can't have escaped all the stories about Brad and Angelina and it looks like the situation has taken a toll on her.

'While her collapse was blamed on heatstroke everyone thinks it is more down to stress than anything else.'

Yesterday it was revealed that Pitt, 42, had accompanied Miss Jolie to Ethiopia where she picked out a baby daughter to adopt.

They are due to return to Miss Jolie's English home with her new daughter, fivemonth- old Zahara Marley Jolie, in the next few days. Reports that Pitt and Miss Jolie were more than friends surfaced almost a year ago, when they were making the movie Mr And Mrs Smith.

Both denied the claims, but since Pitt broke up with Miss Aniston at the start of the year he has been spending an increasing amount of time with Miss Jolie.

The pair were seen on holiday in Kenya in May and they were pictured again last week in the grounds of Miss Jolie's Buckinghamshire mansion.On both occasions Pitt, who has often talked about his desire to have a family, was playing with Maddox, Miss Jolie ' s three-year-old Cambodian adopted son.

Miss Aniston was said to be particularly hurt by a photoshoot the pair took part in to publicise their film for a magazine, which pictured them playing happy families with a host of children.