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The mother-of-five had posted about feeling unwell to her Instagram account while she waited for the results to come through, explaining she was "praying" they had the flu.
In a post on Friday, Katona shared the words: "Tested positive!"
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"Absolutely heartbroken! Sending love and light to all those effected," the former Atomic Kitten star wrote in the caption.
She added in another Instagram Story: "Never felt so poorly! Both Ryan and I are held up in the bedroom. My poor children. I honestly don't know what to do.
"For all of those who don't think Covid is real, think again!!!."
Katona currently lives with four of her five children; Lilly-Sue, 17, Heidi, 13, Max, 12, and Dylan-Jorge, six.
Her eldest daughter Molly, 19, whom she shares with first husband Brian McFadden, is currently attending university in Dublin and is set to spend Christmas with her father's family in Ireland.
She’s previously said she was struggling with the thought of not seeing her firstborn until 2021.
Katona became engaged to Mahoney in the summer during a family holiday to celebrate her 40th birthday.
In an appearance on Loose Women back in September, Mahoney said he felt like proposing was a “long time coming” and revealed he spoke to Katona’s children before popping the question.
She was previously married to Heidi and Max's father Mark Croft and Dylan-Jorge's late dad George Kay as well as McFadden.
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