Former X Factor judge Cheryl, 36, said she realised she was “at risk” after women came forward claiming they had slept with Ashley, 37.
After learning about the reports Cheryl said she got tested and was thankfully “all clear”.
In her 2012 autobiography titled My Story, obtained by The Mirror, she wrote: “I had to face the fact that Ashley’s infidelity had been putting me at risk for a long time, and I had to put my mind at rest.
“I was given the all clear, but my emotional health was still in so much danger.”
Cheryl insisted she initially thought the women accusing Ashley of cheating were lying, but revealed details about him which were not of common knowledge.

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She added: “One girl said they drank rosé wine in a hotel bedroom together, and that Ashley smoked.
“He does like rosé wine, and at first I told myself she could have seen him drinking it in the bar rather than sharing a bottle with him in the bedroom.
“The smoking, though? He’s a footballer and this wasn’t something he did in public. Hardly anybody knew he smoked.”
The Love Made Me Do It hitmaker added that women also said he liked “hand holding in bed”.
She continued: “That hit a nerve, a big one.
“The description ‘like relationship sex’ was so painful to read I blocked it out totally; I couldn’t deal with it.
“I pushed the papers away, feeling sick at the smell of the newsprint, and then I actually vomited.”
Back in 2010, Cheryl and Ashley divorced after four years of marriage.
In 2014, she married her second husband Jean-Bernard Fernandez-Versini after three months of dating.
The former couple split in 2016.
Later that year, it was revealed she was dating Liam Payne, 25.
Last year, they had their first son together, named Bear.
Earlier this year, the pair announced they had split up via their Twitter pages.
In view of her six million followers, she commented: “We are sad to announce that we are going our separate ways. It’s been a tough decision for us to make.
“We still have so much love for each other as a family. Bear is our world and we ask that you respect his privacy as we navigate our way through this together.”