Jennifer Aniston jenkimjohn.jpg The Daily Mirror reports that, after Jennifer Aniston spotted Kimberly Stewart hanging around backstage at John Mayer's Hard Rock Calling concert last night in London, she flipped out - and had John kick Kim out twice!

An Attempt At Civility
The first booting came courtesy of Mayer, who was trying to defuse the hostile situation by having his security escort Kim from the premises.

Jen, however, couldn't resist adding insult to injury - and made sure to give Kim the stink-eye as John's security hauled her off!

If At First You Don't Succeed...
Kim, however, would not be denied, sneaking back in ten minutes later to snap some pics of John from the side of the stage.

And, just to add insult to injury, Kim did her best to cheekily catch Jen's eye while she snapped away!

"Is This Because Of Her?"
Jen, predictably enough, hit the roof - in fact, the tension between the two women was so pronounced that Mayer had to have his security haul Kim off a second time!

According to the Mirror, Kim didn't go quietly, either - as she was being dragged off, witnesses heard her wailing "Why doesn't he want me here? Is this because of her?"

All Angelina's Fault?
According to a source, Jen's jealousy has its roots in the past - specifically, in Angelina Jolie stealing Brad Pitt away from her back in 2005.

"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," a source tells the Mirror. "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."

Hey, we feel for you, Jen, but this seems like a slightly immature way to handle the situation - hopefully she does a better job the next time one of John's dozens of exes suddenly shows up!