Singer Natasha gave birth to her fourth child, daughter Ella, in September and she is horrified that someone would make such a remark.
Katie made the jibe about the star's weight during an appearance on TV show The Wright Stuff and Natasha responded by tweeting: "Today I was called fat by @KTHopkins on TV, well considering my baby is 5 months old, I look & feel bloody great!"
Natasha has since given Katie a further piece of her mind in her latest blog for BabyCentre, calling the Celebrity Big Brother runner-up is "toxic".
She writes: "It was to my complete horror I heard that Katie Hopkins branded myself and fellow bandmates 'chubby' on a TV show this week.
"Luckily, I'm old enough and confident enough in my own skin to brush her idiotic comments aside, but the sad reality is, there'll be other women, especially new mums who will feel under pressure by her comments.
"If she feels it's justified to call me 'chubby' despite the fact I'm a new mum and a size 8, the woman is clearly very harmful and the less exposure she gets the better."
Natasha adds: "What's worse is that she is a mother, does she really believe her own children will be impervious to cruel jibes and insults – what a shame that her legacy will be so toxic and negative."
Since the Celebrity Big Brother final last week, Katie has found herself coming under fire from all angles thanks to her acid-tongue.
On Monday, Katie came to blows with Coleen Nolan during an interview on Loose Women. Coleen took her to task over hurtful comments she had made about her sister Linda's appearance last year.
Since then, Katie has responded to the spat in her newspaper column and on Twitter, while Coleen's sister Anne has also waded in to the row.
Earlier today, CBB winner Katie Price branded Katie Hopkins a "disgusting human being" during an interview with This Morning.
Referring to the Coleen spat, Katie Price said: "If I was her mum and dad I would be ashamed of her. She has no respect for anyone. Her behaviour is disgusting."
This came after Katie Hopkins lashed out at Katie Price to Reveal, saying: "She's a nobody with a pair of t*ts and those t*ts aren't that great either."
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