Lillie had been dating Bear when he entered the CBB house, but their relationship broke down on the show as Bear declared he wanted to be single and publicly moved on with his housemate Chloe Khan.
He went on to win the show and during an appearance on ITV's Loose Women, Bear appeared to claim Lillie had been 'unfaithful' to him during their relationship.
She has now strongly denied this.
He had been talking to Katie Price about wanting kids of his own in the future, and she asked him if he had ever been hurt in the past, as she thinks he puts his guard up when it comes to women.
Bear claimed he had and told her: "The past two girls I've been with in my life, they've cheated on me and it's bang out of order. I'm getting labelled a cheat and this and that, no.
"Unfortunately, the last two birds I've been with did the dirty on me. The next girlfriend I do have, I'll still treat them as well as I did them, but hopefully it works out and I get married."
Bear then later tweeted: "Had a suspicion about @LillieGregg .. She jumped into bed with @rossworswick while I was seeing her .... #ruthless #justfoundout."
He has since deleted his tweet.
Taking to Twitter in response, Lillie categorically denied Bear's claims she had cheated. She tweeted: "Wow how dare you..Quite happy to go to the extent of a lie detector test on this one. Theres only one cheat and it certainly wasn't me."
She added in a second tweet: "Categorically not true. That is my only comment."
When contacted by Reveal a rep for Lillie denied there was any truth in Bear's claims. We have also contacted a rep for Bear.
Wow how dare you..Quite happy to go to the extent of a lie detector test on this one. Theres only one cheat and it certainly wasn't me.— Lillie Lexie Gregg (@LillieGregg) August 30, 2016
Categorically not true. That is my only comment.— Lillie Lexie Gregg (@LillieGregg) August 30, 2016
Lillie and Bear had initially met while filming for series five of Ex On The Beach in April, earlier this year. They went public with their romance a month later and dated for several months, until Bear broke off their relationship while in the CBB house.
He had told his housemates he no longer thinks Lillie is 'the one' anymore and claimed he 'doesn't have time' for a girlfriend. Bear then struck up a romance with Chloe and the pair had viewers divided over their steamy antics on the show.
Lillie, meanwhile, told fans there was "no going back" for her and Bear, and viewers got to see her confront Bear in the house over his behaviour. She told him she had been "embarrassed and humiliated" by him.
Bear never responded to Lillie during her brief stint in the house, but he did later break down in tears and confess that he thinks Lillie had a "lucky escape" from him.
Since then, he has claimed that Chloe is the only girl he is now interested in. He addressed their romance on Loose Women and told the panel: "What it is with Chloe is she's the nicest girl I've ever met in my whole life. Who knows what it might bring? I don't want anyone else for now but I will take it nice and slow."
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