A source said: 'After five years of this Katie really felt like she was going crazy and that she was actually turning into the robot that the press had always made her out to be.
'Katie has actually got a great personality and she used to be spunky and feisty. She changed so much when she was with Tom, she became downtrodden and insipid.
'In the end it just got too much, she was sick of it and decided she had to do something. Basically, she grew up and lost the starstruck goggles she had been wearing.'
Katie is reportedly seeking full custody of their six-year-old daughter Suri after beginning to question her life with Tom and his control of their decision making.
Indeed, the row over his birthday followed another bust-up over what Miss Holmes felt were embarrassingly bad taste pictures of him on the cover of W magazine last month.
He was dressed – or rather undressed – as the rock star Stacee Jaxx, the character he plays in Rock of Ages. Two half-dressed blondes were wrapped around him, one licking his face.
Miss Holmes, a nice girl from Ohio who is nevertheless very aware of why Cruise feels the need to play the macho card in public, was apparently ‘speechless’ with disgust and felt the pictures laid both of them open to ridicule.
The bigger picture is that this is the end of the third of Cruise’s marriages and a spectacular failure of his strategy to relaunch himself as a ‘regular guy’.
And if the union was supposed to cease gossip about Cruise and his personal life, in particular rumours of his homosexuality – always denied – it failed utterly.