The presenter quit as co-host of the ITV daytime show alongside Phillip Schofield in 2009 after 10 years at the helm.
Speaking about her decision to leave on The Ray D’Arcy Show on RTÉ Radio 1 on Friday, Fern explained she had stopped enjoying working on the show and “something happened” on the morning she resigned that prompted her to hand her notice in.
“I began not to enjoy it so much and the morning I resigned, I didn’t know I was going to resign,” she said.
“Something happened and I just thought, ‘That’s it really’ and I walked away and resigned.
“I was treated pretty poorly, actually. And after a while I just thought, ‘Sod it’.”
HuffPost UK has contacted This Morning for comment and is awaiting a response.
Fern also reiterated previous comments that her decision to quit was not prompted by reports Phillip was being paid more than her on the show.
She said: “There was also a persistent rumour that I left because Phillip was being paid more than me and I always say to people, ‘Why would I leave a show to go to nothing if I was worried about money?’”
She explained: “It was all gastric band-gate. It ruffled a few feathers, and I think perhaps I became a bit of a liability to ITV. I really don’t know.”
Fern revealed that she’d undergone the procedure at a time when she was the face of Ryvita, leading some critics to suggest she’d “lied” about the way she lost five stone, which the presenter has always refuted.
The presenter made a brief return to This Morning in 2018 for the show’s 30th anniversary celebrations, and threw shade at her former TV home for failing to invite her to a Bafta celebration.
It later transpired that she had been sent an invitation, but it had not been passed along to her by her team.
This Morning airs weekdays at 10am on ITV.