The two had reportedly been at odds since filming the show together, with the demise of any prospects for a third "Sex and the City" film bringing the animosity back to the surface, reports hollywoodreporter.com.
Cattrall took to Instangram to vent her anger on Saturday.
"I don't need your love or support at this tragic time Sarah Jessica Parker," she posted.
In the caption, she called Parker a "hypocrite" and "cruel".
She said: "Let me make this very clear. (If I haven't already) You are not my family. You are not my friend. So I'm writing to tell you one last time to stop exploiting our tragedy in order to restore your 'nice girl' persona."
According to hollywoodreporter.com, Cattrall was likely referring to the recent death of her brother Chris, which Parker discussed at the Paley Centre for media's "An Evening With the Cast of Divorce" in New York on Thursday.
In the article, a clique that excluded Cattrall is described as having been formed on the set of "Sex and the City" particularly after creator and producer Darren Star left and Parker's friend Michael Patrick King took over, which led to Cattrall's reluctance to participate in the first "Sex and the City" film.
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