Former Mayor Rudy Giuliani and Mayor Mamdani had a tense – but civil – exchange at the 9/11 memorial service Friday, with an expert revealing the message “America’s Mayor” passed on to Hizzoner.

“I prayed for you,” Giuliani, who is a devout Roman Catholic, told Mamdani as the two men shook hands, according to Jeremy Freeman, a UK-based expert lipreader. “Good job. OK.”

New York Mayor Zohran Mamdani, right, passes former New York Mayor Rudy Giuliani ahead of a ceremony commemorating the 25th anniversary of the Sept. 11, 2001, attacks at the National September 11 Memorial. Barry Williams/Pool The Daily News via AP

The greeting — which came at Ground Zero after Giuliani joined growing calls for Mamdani to skip the memorial services — was awkwardly fraught, body language expert and behavior analyst Traci Brown told The Post.

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“Giuliani’s eyebrows [are] up in recognition and acknowledgment. But his frown grows the longer they shake hands. So he’s not happy about the connection,” Brown said after viewing footage of the interaction.

“Mamdani is leaning in and wants to connect. After he’s not feeling so good about it. And works to counteract that feeling by making himself confident. That’s what the hand on his hip is,” she added.

The pleasantries came after Giuliani, 82, claimed Sunday that Mamdani “doesn’t agree that September 11 was an Islamic terrorist attack on the United States of America” before launching on an anti-Muslim conspiracy-laced rant.

New York City Mayor Zohran Mamdani shakes hands with former NYC Mayor Rudy Giuliani. Giuliani helmed the city during the 9/11 attack. CNN

“No question,” he said during an interview with Newsmax — saying that  Mamdani attending 9/11 memorials “offends me.”

Mamdani on Tuesday took a subtle dig at his predecessor, who led New York City during the Sept. 11, 2001, terror attacks.

“People got sick because the leaders they trusted lied and told them they were safe to breathe in toxic air,” Mamdani said, without outright naming anyone, as City Hall released 170,000 long-hidden documents on air quality risks after the attacks