On Sunday, it was reported that Kay had passed away at the age of 39 after being found collapsed at home.
Katona and Kay were married for three years from 2014 until 2017. Their daughter, Dylan-Jorge, was born in April 2014.
Following the news of Kay's death, fathers' rights organisation Fathers 4 Justice posted a tweet claiming that Katona had denied Kay access to their five-year-old daughter, and stated that the former Atomic Kitten bandmember has "blood on her hands".
Katona's 17-year-old daughter Molly McFadden expressed her fury over the tweet, describing it as "disgusting".
Tragic news about the passing of George Kay who came to Fathers4Justice for help. He was heartbroken after @KerryKatona7 denied him access to daughter Dylan-Jorge. Katona’s not ‘heartbroken’. She has blood on her hands. Matt O’C #RIP https://t.co/3dcKUSJ5m1— Fathers4Justice (@F4JOfficial)July 7, 2019
I suggest take this tweet down, how dare you make statements this disguisting at such a vulnerable time, your accusations are innacurate nd extremely insensitive. I truly hope you never find yourself in this kind of situation. Vile words from a vile person you should be ashamed.— Molly (@123_mollymc)July 7, 2019
"I suggest [you] take this tweet down, how dare you make statements this disgusting at such a vulnerable time," McFadden tweeted.
"Your accusations are inaccurate and extremely insensitive."
The Fathers 4 Justice tweet was signed "Matt O'C", implying that Fathers 4 Justice founder Matt O'Connor penned the post.
McFadden described the words used in the Fathers 4 Justice tweet as "vile".
Several Twitter users similarly criticised the fathers' rights organisation's tweet.
"You really are disgusting. There is no justification for this tweet," one person wrote.
"This is disgraceful and you should delete this," another added.
In response, O'Connor tells The Independent that he felt it was "appropriate to raise the issue" of Kay's death after the former rugby league player contacted Fathers 4 Justice in March 2018.
O'Connor says that he didn't believe his statement regarding Katona having "blood on her hands" "went far enough", adding that the issue "shouldn't be censored".
The fathers' rights campaigner describes the difference between mental health treatment for mothers and fathers as "chalk and cheese", stating that in his opinion, society "supports mothers and abandons fathers".
On the subject of McFadden's tweet, the Fathers 4 Justice founder says: "It's inappropriate for a 17-year-old minor to get involved in complex adult issues."
The Independent has contacted representatives of Katona for comment.