The model, 33, was horrified when she found messages to other women on the rugby player's mobile phone last weekend, according to The Sun.
The former Big Breakfast presenter's discovery came just days after they returned from holiday in Turkey.
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It's over... again: Kelly Brook and Danny Cipriani, pictured in London in June, have reportedly split up for the second time
When Kelly found the messages, she threw Danny out of her London home and has since deleted all recent photos of him from her Instagram page.
Sales manager Stacey Simcox, from Birmingham, claims she was bombarded with sexy messages and photos from Danny after meeting him eight months ago.
Stacey told the paper: 'He'd send me filthy messages about what he wanted to do to me and begging to meet up for sex.
Unfaithful? Kelly and Danny in London on June 29 - the last time they were photographed in public
Stacey said she refused Danny's requests to meet up, even receiving an invitation as recently as July 27 - the day he flew to Bodrum with his famous girlfriend.
A friend told the paper: 'Danny is absolutely devastated. He just can't believe what he's done - he just wants Kelly back.'
Calm before the storm: Kelly posted this photo of the couple in Turkey just over a week ago - which has since been deleted