Kate Hudson and Cameron Diaz are fighting over Alex Rodriguez
Cameron is dating the baseball star which has infuriated Kate - who was in a relationship with Alex from May to December last year - and she now "hates" the `Knight and Day` actress.
Kate believes Cameron is trying to get her back for sleeping with Justin Timberlake just days after the pair split in early 2007.
A source told Us Weekly magazine: "Kate thinks it`s payback pure and simple. Cameron was actually in a serious long-term relationship with Justin.
"She thinks it`s a joke Kate would be mad. Kate is only upset because she hates being single."
Now, the 31-year-old actress has started getting personal, and claims Cameron, 37, is an "ageing" star who is struggling to keep her youthful looks.
The source said: "Kate thinks Cameron is an ageing actress struggling to remain sexy and relevant."
Recently Alex - who plays baseball for the New York Yankees - is believed to have banned Cameron from coming to his games because he wants to keep things casual with her.
An insider said: "He doesn`t want what happened to him and Kate to happen between him and Cameron. Kate was at every New York game and then some and even went to Alex`s game practice. Things got too clingy, too fast."