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.”