Cattrall's brother, Chris Cattrall, was found dead on Feb. 4 after having previously gone missing.
Parker, who played Carrie on the hit show, expressed her sympathy to Cattrall in a comment on Instagram. She also spoke about the tragedy at a Thursday screening of her HBO show Divorce.
“I can't begin to know how her family is managing such a loss. We all send her our love and condolences and grant her the privacy that she's asked for," Parker told Extra.
But on Saturday, Cattrall took to Instagram to reject Parker's condolences.
"My Mom asked me today 'When will that @sarahjessicaparker, that hypocrite, leave you alone?'" Cattrall wrote on Instagram. "Your continuous reaching out is a painful reminder of how cruel you really were then and now.
"Let me make this VERY clear. (If I haven’t already) You are not my family. You are not my friend," Cattrall wrote. "So I’m writing to tell you one last time to stop exploiting our tragedy in order to restore your ‘nice girl’ persona."
Cattrall ended the message with a link to a New York Post article that detailed the bitter, longstanding tension between the former costars — and how it may have sank a possible third Sex and the City movie.
Parker did not immediately respond to request for commment.
Last September, Parker confirmed there would not be a third Sex and the City movie, telling Extra, "It's over... We're not doing it."
"I'm disappointed," Parker said. "We had this beautiful, funny, heartbreaking, joyful, very relatable script and story. It’s not just disappointing that we don’t get to tell the story and have that experience, but more so for that audience that has been so vocal in wanting another movie.”
The Daily Mail had previously reported that the stars had been ready to start filming the third movie, but it was shelved after Cattrall demanded Warner Bros. also produce other movies she was working on.
Cattrall denied the reports, telling Piers Morgan that none of her former costars had reached out to her when rumors began circulating that she was being blamed as the final nail in the movie's coffin.
“The answer was always no,” said Cattrall. “I never asked for any money, I never asked for any projects. To be thought of as some kind of diva is ridiculous.”
She also said she didn't know the last time she'd spoken with her former costars.
“Nobody ever picks up the phone and tries to contact you and say, ‘How you doing?‘ That would have been the way to handle it,” she said. “This is, it feels like, a toxic relationship.”
By the end of the Sex and the City TV series, the tabloids were full of talk about drama between the two stars, which was reportedly linked to Parker making significantly more money than Cattrall.
They were reportedly no longer on speaking terms by the time they started filming the movies.
The New York Post article shared by Cattrall cites a claim from a friend of hers who reportedly said "Kim does not want to ... do the film."
“She feels she has been treated horribly by Sarah Jessica Parker for six years," the friend reportedly said.