Kristen & Rupert were caught ‘kissing like teenagers’ on July 17 — just five days before Kristen & Rob flaunted their love at the 2012 Teen Choice Awards!

Robert Pattinson and Kristen Stewart are one of our favorite celebrity couples. We’ve loved watching them in love, on-screen and off, so much that this latest news on their relationship is devastating: Kristen cheated on Rob.

People reports that Kristen, 22, had a “brief fling” with Rupert Sanders, the married director of her recent film Snow White and the Huntsman. “Kristen is absolutely devastated,” a source tells the magazine. “It was a mistake and a complete lapse in judgement.”

“She wasn’t having an affair with Rupert,” the source continues. “It was just a fleeting moment that shouldn’t have happened. She never meant to hurt anyone. She’s a good person who just made a bad choice.”

In a separate report, Us Weekly claims the encounter happened July 17 in Los Angeles. According to the magazine, Rupert and Kristen were caught by photographers during a “marathon make out session.” One eyewitness even tells the magazine, “It seemed like they couldn’t get enough. … Kristen was sitting with her back up against the driver’s-side window [of her black Mini Cooper] and the guy was kissing her entire body.”

Kristen and Rupert only stopped kissing when they thought they’d been spotted — but quickly resumed making out once they felt they were in the clear. From that point, the magazine reports, Kristen and Rupert drove to several different locations in Hollywood to escape the paparazzi. They eventually ended up at Pacific View Trail, where they parked her car and got out to enjoy the view.

“She was swept up in the moment,” an onlooker tells the mag. “A few people would walk by, and as soon as they heard a voice, they would split up and walk in other directions.”

When they were finished, Kristen drove Rupert home — he lives with his wife of seven years, 33-year-old British Vogue model Liberty Ross, and their two children, ages 7 and 5 — parking three blocks away just to be safe.

SWATH began filming in Aug. 2011 and wrapped in December, with the film having been released this past May. We have to wonder if this is something that began months ago, when Kristen and Rupert were working together for those four months, or if it truly is a recent development, as People claims.

A source close to the couple admits that Rob worried about Kristen during their time apart while she was filming, especially when she wouldn’t “call him back” for days at a time.

We’re especially shocked by this news because of how in love Rob and Kristen appeared July 22 at the 2012 Teen Choice Awards — just five days after her alleged tryst with Rupert!

Rob and Kristen have been together for the past four years, since meeting each other on the set of the first Twilight film. The two even live together. While we don’t know Kristen’s stance on cheating, Rob has been very vocal about how he’s against cheating, even saying how he doesn’t understand it.

“There is one thing I’ve never understood: why people cheat,” he said. “My parents met when my mom was 17 and my father 25; they are still together and seem very happy. I grew up believing that you can be together all of your life.”

In fact, one source even tells Us Weekly that Rob “wants to spend the rest of his life with” Kristen. He was planning on proposing!

“Rob worships the ground Kristen walks on and would marry her in a second,” a friend tells the mag.

HollywoodLife.com has reached out to Rob, Kristen and Rupert’s reps, but have not yet received a response.

— Billy Nilles

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