Glamour model Danielle McMahon went out with the self-proclaimed sugar daddy for four months before he entered the house in June.
Speaking to The Scottish Sun newspaper, Danielle claimed that almost every aspect of Dexter's Big Brother life was fake.
"He’s a real manipulator, he plays mind games and he mixes up stories. He’s a professional liar," she told the tabloid this week. “I can’t even watch the show anymore because I can’t stand his lies.
“Everything about him is completely fake. He said he’s slept with 2,000 women, but I know for a fact that he’s only slept with eight."
Danielle said Dex's claims of being a "notorious" sugar daddy, strip club owner and PR guru were all made up.
“Everyone thinks he’s a sugar daddy and that he’s loaded — he’s not. He lives in a semi in Liverpool," she explained. “He claims to have owned a strip club, but he hasn’t. He was a waiter in a strip club. He also said he was a celebrity magician. That’s another lie, he used to work in Hamleys toy shop.
"His main source of income was from papping Z-list celebrities. He just waits outside clubs for hours and makes money from that. When I met him back in December he had about 16,000 followers, and he told me three-quarters of them were fake.”
Even Dex's mum confessed that a lot of what he said to get into the house was "exaggeration", such as his tales of being London's highest paid male escort.
"I'm not sure about the male escort bit - I think that was an exaggeration," mum Ellen said last week. "I think years ago someone wanted to do an article.
"If someone says: 'I'll give you £6,000 for your name and picture', you'd say yes wouldn't you? I think it was actually more like £25,000."