WASHINGTON, DC - SEPTEMBER 06: Former New York City Mayor Rudy Giuliani arrives for an address at the National Press Club September 6, 2011 in Washington, DC. Giuliani spoke on the state of U.S. security in the 10 years since the September 11 terrorist attacks. Win McNamee/Getty Images

The plot thickens in Rudy Giuliani's increasingly bitter divorce proceedings.

Back in April, the former New York City mayor and his wife Judith Nathan announced they were splitting after 15 years of marriage.

No reason was given in his statement at the time.

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On Wednesday, we finally think we know why: a mistress.

Multiple sources tell The New York Post that Giuliani cheated on his wife with a married New Hampshire hospital administrator and when Nathan found out, she filed for divorce.

The presidential lawyer, 74, denied he and Maria Rosa Ryan, 53, had an affair and that anything that happened between them was after he and his third wife had separated.

“My husband’s denial of the affair with the married Mrs. Ryan is as false as his claim that we were separated when he took up with her,” Nathan said in a statement to The Post.

The onetime nurse filed for divorce April 4, mere days after Giuliani publicly stepped out with Ryan in front of TV cameras when he visited her hospital to discuss cybersecurity measures for patients there.

The relationship between the two certainly seems tight.

When Donald Trump's attorney jetted to Fort Lauderdale last month, he was helping defend Ryan's daughter, 32 year old Vanessa Ryan, in court against charges of car-insurance fraud. Giuliani appeared at Broward County Courthouse in Fort Lauderdale on her behalf, reported CBS4.

The airline industry worker was accused of purchasing Progressive insurance online at the scene of a 2016 accident and providing false information to the insurance company.

The Daily Mail reports that Giuliani described Ryan as his "personal assistant."

"I came to show the court she is just a young woman who made a mistake," he told the media outlet, which added that a second court date for this case is set for July 9.

This story was originally published June 13, 2018 11:52 PM.