Ex-New York City Mayor Rudy Giuliani emerged from a coma Monday and was talking and alert as he remained hospitalized in Florida while recovering from pneumonia, Big Apple billionaire pal John Catsimatidis said.

Catsimatidis said he received the uplifting news from  a close former aide to the 81-year-old ex-“America’s mayor’’ Monday afternoon.

“He’s talking, he’s alert. To me, that’s great news,’’ the supermarket and media mogul told reporters.  

Giuliani’s shocking weekend hospitalization occurred after he was stricken with the respiratory illness, said his business partner, Tom von Essen, who served as the city’s fire commissioner during 9/11.

“Rudy had a tough weekend. He had pneumonia,” von Essen told The Post, calling Monday “an important day’’ in terms of Giuliani’s recovery.

Giuliani’s spokesman, Ted Goodman, confirmed the ex-mayor was recovering from pneumonia.

He was now breathing on his own, with his family and primary medical provider at his side, the spokesman said.

“Mayor Giuliani is the ultimate fighter — as he has demonstrated throughout his life — and he is winning this battle,” Goodman said.

“He’s alert and breathing on his own. Today was a good day and tomorrrow should be even better, barring any unforeseen setbacks,” another source close to the former mayor said.

Giuliani’s doctor, Maria Ryan, echoed Goodman, describing the former mayor as a “fighter” but told Fox News “he did have a priest come anoint him.”

“And all the prayers from around — it’s like a miracle. This guy’s got 9 lives, today he’s doing much better.”

The illness is tied to a condition stemming from Giuliani’s experience as mayor during the Sept. 11, 2001, terror attacks, the rep said.

“On September 11th, Mayor Giuliani ran toward the towers to help those in need, which led to a restrictive airway disease diagnosis,” the spokesman said.

“This disease adds complications to any emerging respiratory issue, and the virus quickly overwhelmed his body, requiring mechanical ventilation to maintain his blood pressure.”

The update on Giuliani’s condition capped a whirlwind day following the disclosure Sunday that the close ally of President Trump was in critical but stable condition with a then-publicly undisclosed ailment.

Trump led a chorus of well wishers for Giuliani, which swelled Monday to include lefty Mayor Zohran Mamdani.

“Absolutely, I’m wishing strength and recovery to former Mayor Rudy Giuliani and his loved ones during this difficult time. And I hope that his recovery is steady, and I hope that his family finds peace in one another during this time,” Mamdani said at an unrelated press conference. 

“I think former Mayor Giuliani is someone that we, as New Yorkers, know well, and he’s been a fixture in our city’s politics and public life for so many years, and I know that many New Yorkers are concerned by reports he is in critical condition and so we do keep him and his family in our prayers at this time,” he told reporters. 

Former Gov. George Pataki told The Post that Giuliani had been set to attend an event for his charity Thursday.

“I was looking forward to seeing him … and being able to talk at length,’’ Pataki said. “I haven’t talked to him in a few months.

“We were great partners for the city and the state for seven years together, and we were able to just do a tremendous amount to make the city and state a better place by working together.

“So obviously now we just hope he gets better,’’ Pataki said.

“It was just a shock’’ to learn Giuliani was even hospitalized, the ex-governor said.

“You just take for granted that figures that have such a large profile in our state and our country will be around for a long time,’’ he said.

WABC radio host and longtime city journalist Dominic Carter, in extending his best wishes to Giuliani at the media scrum with Catsimatidis, said,  “History is going to judge [Giuliani] as the greatest mayor of New York City ever.”

Catsimatidis was asked at the press conference about how his friendship with Giuliani has lasted, even after the former mayor sued him for giving him the ax from the mogul’s radio station, WABC.

“Friends for 40 years, brothers for 40 years,’’ the wealthy businessman said.

“Do brothers have arguments? Of course, we did. We kissed and made up.”

— Additional reporting by Marisa Shultz and Craig McCarthy