Rudy Giuliani’s feisty soon-to-be ex-wife Judith Nathan Giuliani is writing an explosive book about her estranged husband and his inner circle of powerful allies.

A source close to Judith said she has been in talks with at least three publishing houses about her book, which promises to lift the lid on the private side of President Trump’s prevaricating personal lawyer and the wealthy circles he operates in.

The source said, “This isn’t going to be a salacious ‘In bed with Rudy’-type book, but that doesn’t mean she isn’t picking up the poison pen. Judith’s book will talk about how ‘America’s Mayor’ and his powerful friends operate, the secret deals and secret handshakes, what it is like being on the inside with Manhattan and DC’s power brokers. There is also much to discuss about Rudy’s relationship with President Trump, and how Rudy struggled after his own political ambitions to be president failed.”

Judith filed for divorce in April after 15 years of marriage — and shortly after she says she learned he was cheating with hospital administrator Maria Ryan, which he strongly denies.

She has hired powerhouse Manhattan divorce lawyer Bernard Clair, and it won’t have escaped him or Judith that the prospect of personal details emerging about Rudy and his inner circle could be a strong bargaining tool to get what she wants in the eventual settlement — which would likely include a non-disclosure agreement to stop her dishing the full dirt on her soon-to-be ex.

Firing a warning shot, the qualified nurse just said in an interview with New York Magazine about Rudy, “The man that he is now is absolutely not the man he was when I married him … For a variety of reasons that I know as a spouse and a nurse, he has become a different man.”

She wouldn’t explain how or why he changed — only that it was “an ongoing process that began when he lost the presidential campaign,” and he was once a straight talker who is now “dissembling” as Trump’s personal lawyer. In 2008, Giuliani blew his own presidential hopes when he focused on Florida, but came in third in the primary and had to withdraw and endorse Sen. John McCain.

Giuliani — who was seen getting cozy with Ryan at a New Hampshire hotel and has also traveled with her — has insisted that the relationship was purely platonic and that he has instead been dating GOP fundraiser Jennifer LeBlanc since the split.

But Judith doesn’t buy it and insists he was cheating with Ryan — claiming she’s seen recent cellphone bills that show constant communication between the two.

Associates of Giuliani have dismissed Judith as a “detestable person” who can’t be trusted. “She’d cut your throat for a dollar,” one told New York mag.

Judith’s attorney Clair didn’t return calls and reps for Giuliani could not be reached by deadline on Monday.