In Pictures: Jennifer Aniston Gets Kimberly Stewart Removed From John Mayer Concert

Jennifer Aniston reportedly had Kimberly Stewart thrown out of new boyfriend John Mayer's concert when she tried to sneak backstage.

The former 'Friends' actress -- who has been romantically linked to the 'No Such Thing' hitmaker for several months -- was said to be furious when Kimberly, who has history with John, turned up backstage before his performance at Hard Rock Calling in London's Hyde Park on Sunday.

And to defuse the situation, John asked security to remove Kimberly.

A source says, "Jennifer spotted Kimberly and asked John what she was doing there.

"John and Kim know each other from clubbing in LA, but Jennifer doesn't want anyone around who reminds her that he used to be a player.

"She has fallen head over heels for John, but she's scared it will all go wrong again.

"Another woman stole her man before when Angelina Jolie started dating Brad Pitt -- she couldn't bear it to happen again."

However, just 10 minutes after being told to leave, Kimberly was back at the side of the stage and started waving at John, so she was removed for a second time.

The source added to Britain's Daily Mirror newspaper, "She had been told twice by security that she would be removed but she stood there bold as brass.

"Jennifer was on the opposite side of the stage and John felt like piggy-in-the-middle.

"He saw the tension and told his bouncers to get rid of her at all costs.

"Kim was pulled off the stage and escorted through the Hard Rock VIP tent with a face like thunder, shouting: 'Why doesn't he want me here? Is this because of her?'

"She totally embarrassed herself, but Jen looked relieved."

Meanwhile, Aniston, 39, has reportedly banned Mayer, 30, from having contact with ex-girlfriend Minka Kelly, 28.