Cameron Diaz and Justin Timberlake split because the singer cast Scarlett Johansson in one of his music videos, it has been claimed. Cameron - whose four-year relationship with the SexyBack (Video) singer came to an end shortly before Christmas - was allegedly furious when Justin chose Scarlett to play his love interest in the promo for his song What Goes Around. The couple's relationship was already struggling and Justin's decision casting decision was the final straw.

A source told Heat magazine: "When Justin cast Scarlett, Cameron felt it was the first time another person was involved. She can get very angry and very jealous. When she knew the other person was possibly Scarlett, she was furious. The two women have never been good friends, plus Scarlett had a relationship with Jared Leto, who Cameron had previously dated for four years."

Since the break-up, Cameron - who has recently been linked to champion surfer Kelly Slater - has apparently turned to her Charlie's Angels co-star Drew Barrymore for support.

The source added: "The two girls have a lot in common, as Drew just broke up with her boyfriend of five years, Fabrizio Moretti. Cameron is emotionally distressed but Drew told her, 'Time heals all. Justin was probably not the right person for you.' "

Justin and Scarlett were recently spotted partying together at the post-premiere party of his new film Alpha Dog at the exclusive Social Hollywood club.