Katie, 36, posted a message during Manchester City goalkeeper Joe's big day, which many took to mean she had history with him.
The mum-of-five wrote: "All Harts go out to the married couple is he going to tell her the truth about us xx [sic]."
Former glamour model Katie quickly deleted the tweet, but not before it caught a lot of attention.
However the new Mrs Hart is said to be unbothered by Katie's apparent dig.
A source told The Sun: "Kim couldn't care less. She thinks Katie's a clueless bimbo.
"She has no concerns about Joe, and told friends 'In her dreams!' She probably wishes she could get her hands on him but she can't."
It is claimed that Katie and Joe met in 2010 at a charity event in Cheshire, but the insider added: "Kim knows Joe may have met Katie at a function and kissed her on the cheek but that's as far as it would go."
Kim and Joe, who have 10-month-old son Harlow together, are currently on their honeymoon n Abu Dhabi.