Former “Australian Idol” winner Casey Donovan fell into a “vicious cycle of sex and one-nightstands” after she was duped into a relationship for six years by a non-existent man.

The 25-year-old songstress, who won the second season of the now defunct reality show when she was just 16, has revealed in her book “Big, Beautiful and Sexy” that she unwittingly got engaged to her stalker.

She told New Idea, which obtained excerpts of her book, that she was drawn in by a mysterious man named Campbell on the phone while touring in 2004.

He described himself as a tall, well-built, charming, part-Aboriginal man from Sydney with a “six-pack to die for” and “a smile that would melt your heart.”

“I wasn’t pretty. I was fat. I always said the wrong things and made a fool of myself,” she told New Idea. “What on earth could he see in me?”

Their relationship blossomed, but never progressed. He Campbell always had an excuse when she asked to meet him in real life.

He then introduced her to a friend named Olga, whom she became good friends with. Then Campbell insisted that Donovan sleep with Olga.

“I was so vulnerable that finding someone who was interested in me made me feel on top of the world,” she said, attributing her low self-esteem and history of self-harm for trustfulness.

“I loved that he loved me, yeah. I had never had a boyfriend and it was something I was longing for. I believed everything and I was hopeful and... I was groomed very well.”

It turned out that Campbell didn’t love her because he wasn’t real. The Olga friend that he introduced and whom she had sex with was actually the person behind the deception.

She found out that she was being duped for six years when a SIM card that was supposed to belong to her so-called fiancé was in Olga’s room. Olga then admitted that the whole thing was a lie.

“In the end, Olga did confess that she was Campbell. I finally heard it from the devil’s mouth. But she never came close to explaining why she did it,” Donovan wrote. “How could it go on for so long? How could I be so stupid?”

The Daily Telegraph revealed that real name behind Olga’s identity is Jade Katie Cavanagh who works in group sales at Qantas in Sydney. According to a source, Cavanagh is the woman Donovan is referring to in her book.

However, Donovan’s management refuses to confirm the name.

“Unfortunately I am unable to confirm Olga’s identity as it is not my story, it is up to my client to make that decision,” her manager Jason Williamson said.

In “Big, Beautiful & Sexy,” Donovan admitted that she was desperate to escape the trauma of the six years with Olga. She turned to using dating apps to contact men, losing her virginity at 23 after having sex with a stranger.