"We have been together for five years but they have made me feel like a fool," said the woman who the Herald agreed not to name.
"His underwear is still in my laundry basket."
However, Mullayanov told the Herald he had split up with his partner some time ago although he could not remember exactly when.
"I was single when the show started filming, and I do not reside with my ex-partner," he said.
When contacted by the Herald he denied he was in a relationship with Khanjani. He initially denied writing the explicit messages, saying his Facebook messages had been hacked. He then said the hacking was a privacy issue and he was talking to his lawyer and police.
But his former partner claims their five-year relationship only came to an end this week. She said Mullayanov said he was going to an after-party for the show on Monday but then also failed to come home Tuesday, after completing a day of media interviews with Khanjani.
He told her he was staying at a friend's, she said. When she saw him on Wednesday they had an argument about Khanjani and she forced him to stay in the spare room.
"If he had told me then the truth I would have said 'that's life' and got on with it. But he denied there was anything going on," she said.
On Thursday, she said she looked at the couple's shared laptop which is when she came across the messages.
The Herald has seen the messages but chosen not to publish them.
Both Mullayanov and Khanjani told the Herald that because they were "two single adults, the nature of any messages between us is our own business".
Khanjani has previously coyly shrugged off the rumours of romance between the pair, admitting she had received a lot of questions about the chemistry they shared on stage.
That had led to a misinterpretation of their growing relationship, she had said.
In a statement provided to the Herald, she said the pair considered themselves "best friends".
"Over the course of our time on Dancing With The Stars we became very close and consider ourselves best friends. We often looked to each other for advice and support. It is upsetting that anyone would breach our privacy like this on Tim's personal social media account."
A Mediaworks spokesperson said psychological support was available to all participants both during filming and after the show has aired, as it was with all of the channel's reality shows.
