Since she first clapped eyes on Jamie Burke - on Richard Branson's Caribbean island, Necker - 32-year-old Kate wasted no time getting her claws into the wannabe musician.
Problem is, when they finally became an item, Jamie, 20, hadn't finished with his girlfriend of two years, who was back home in their shared apartment in New York.
The first that 24-year-old model Jessie Leonard heard about her boyfriend's holiday fling with an international supermodel was when she read about it in the newspapers. She was devastated when pictures were published of Jamie kissing Kate during a New Year skiing trip in Colorado.
Now she has fled home to her parents in Australia, where she has gone into hiding and is refusing to talk to Jamie or any of his pals.
"We thought they were going to get married, but now he's gone off with Kate Moss - we can hardly believe it," a member of Jessie's family told us yesterday. "He's just a wannabe rock star who did a couple of modelling jobs and his head got too big.
"We flew her home to Australia because she didn't want to be in New York or in London," says our insider.
"Jessie has been whisked off to a secret location in the far north of Queensland, where she's staying with her mum until the furore dies down. Jamie keeps trying to ring her to try and sort things out, but she's having none of it. "Most of their mutual friends also think he's treated Jessie badly and are giving him a hard time."
And it seems that Jamie himself might be regretting his high-profile romance.
"He loved all the attention, but now he's feeling the backlash - suddenly it's not all fun and games any more," says another source.
3am recently revealed that on Necker Jamie was unaware that Kate, recently in rehab after the Mirror caught her taking cocaine, was making a move on him. In response to her advances he just chatted about Jessie. But she lured him into bed in Colorado and they have since been seen dining out in New York.
That is also where Kate is rumoured to have celebrated her 32nd birthday last weekend. Not wanting to be around people who might be doing drugs, she cancelled plans for a wild party and opted for a low-key dinner instead.