Robert Pattinson has been left "heartbroken and humiliated" after girlfriend Kristen Stewart cheated on him. The heartthrob was stunned when he discovered his partner of four years had been caught kissing director Rupert Sanders - who she worked with on Snow White and the Huntsman - and sources say he is struggling to cope with the news. One source - who saw Rob and Kristen fighting backstage at the Teen Choice Awards in Los Angeles on Sunday - said: "Rob and Kristen were having a long and intense conversation backstage, and he looked miserable, heartbroken and humiliated. She was pleading." Another source added to the New York Post newspaper: "Rob is deeply in love with Kristen and is very jealous when other men hit on her. This will crush him."

'I'm so sorry' After pictures emerged of Kristen and Rupert - who has two children with his wife Liberty Ross - kissing the 22-year-old actress issued a statement saying how sorry she was. Kristen - who started dating Robert after meeting on the set of the first Twilight film -said: "I'm deeply sorry for the hurt and embarrassment I've caused to those close to me and everyone this has affected. "This momentary indiscretion has jeopardised the most important thing in my life, the person I love and respect the most, Rob. I love him, I love him, I'm so sorry."
Rubert also spoke out, saying: "I am utterly distraught about the pain I have caused my family. My beautiful wife and heavenly children are all I have in this world. I love them with all my heart. I am praying we can get through this together.
Meanwhile, Lady Gaga has defended Kristen Stewart's cheating. The 22-year-old actress has publicly apologised to her boyfriend of four years Robert Pattinson after she was caught in a steamy make-out session with her Snow White And The Huntsman director Rupert Sanders and Lady Gaga has weighed in, telling people to leave them alone. She tweeted to her 27.5 million followers: "Geez this kirstew rob stuff is brutal. Makes me sad the way press acts. Hope they're ok (sic)."
Kristen's statement read: ''I'm deeply sorry for the hurt and embarrassment I've caused to those close to me and everyone this has affected. This momentary indiscretion has jeopardised the most important thing in my life, the person I love and respect the most, Rob. I love him, I love him, I'm so sorry." Sources close to the actress insist she wasn't having an affair with Rupert and it was a fleeting mistake. An insider said: "Kristen is absolutely devastated. It was a mistake and a complete lapse in judgment."
Kristen and Robert, 26, have been dating since meeting on the set of Twilight four years ago, in which they play vampire Edward Cullen and his love interest Bella Swan.