Michael Patrick King has claimed Sarah Jessica Parker and Kim Cattrall fell out over pay disparity.
The executive producer of 'Sex and the City' has alleged that the stars of the show and subsequent spin-off movies - who played Carrie Bradshaw and Samantha Jones respectively - showed signs of a waining friendship when Kim asked to be paid the same as Sarah Jessica.
Speaking on the 'Origins' podcast, he said: "The show doesn't exist if Sarah Jessica wasn't the blonde star of the show, that's number one.
"Kim was not at the height of her career, Kristin (Charlotte Yorke) was under her in terms of notability, Cynthia (Miranda Hobbs) was a theatre actress and their contracts reflected that status."
He admitted: "I guess for Kim it didn't matter how much the raise became if there was never parity, but there was never going to be parity."
Michael also claimed that Kim wasn't "mentally" a part of the show's "family".
He added: "As the show progressed, the characters, everybody grew, it became a family.
"Kristin, Cynthia, and Sarah Jessica became one group, and Kim never joined mentally.
"Kristin and Cynthia went in the light, they became those two ladies, they understood it was Sarah Jessica's name, look at the posters."
Kim and Sarah Jessica were reported to be in a feud after it was claimed Kim had been the cause of the third 'Sex and the City' movie being cancelled, due to her alleged diva demands on set.
The actress then publicly slammed Sarah Jessica by claiming she had a "toxic" relationship with her, and later accused her of "exploiting" her tragedy after she sent her condolences to Kim when her brother passed away.
Kim said: "My Mom asked me today 'When will that @sarahjessicaparker, that hypocrite, leave you alone?' 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. So I'm writing to tell you one last time to stop exploiting our tragedy in order to restore your 'nice girl' persona. (sic)"
However, Sarah, 53, has insisted she's "not in a fight" with Kim.
The 'Failure to Launch' star slammed the idea of there being a "catfight" between her and her former co-star - who made scathing comments about Sarah Jessica in the past year - as she has "never fought" with the 62-year-old star.
She said: "If one more person calls this a catfight ... I'm not in a fight.
"I never fought with Kim. I don't have to send any gifts to Kim, because I've never done anything. She has felt perfectly comfortable to say lots of things. That's the beauty of living in a democracy, but I have no apologies, meaning, this isn't a catfight.
"This is someone who chose to talk about something and myself, I remain grateful for her work and the role she played on and off camera for all the years we spent together."