Someone who isn’t Eric Adams secretly acted as mayor as Hizzoner dealt with a mystery illness – and New York City didn’t know for a month, The Post has learned.

Adams admitted Wednesday that he went under anesthesia for a medical test amid his health scare and revealed First Deputy Mayor Maria Torres-Springer briefly took over his duties as mayor of the largest US city.

But the mayor, during his weekly news conference, also wrongly said the test was conducted last week – sparking confusion and a shifting narrative from City Hall about the ailment that kept him uncharacteristically out of the public eye.

City Hall officials later told The Post that Adams actually was put under for a colonoscopy on Jan. 3, more than three weeks before his office announced he’d have a limited schedule to undergo medical tests.

Mayoral spokeswoman Kayla Mamelak added that Adams misspoke when he told reporters he went under last week.

The secret transfer of power to Torres-Springer also raised questions about whether Adams violated the City Charter’s rules on continuity of government, which the mayor denied.

“We did everything we were required to do during the period of anesthesia,” he said.

Adams defiantly maintained that he deserved a right to privacy over his health, but did disclose that the illness involved a “real pain” in his side that required a series of medical tests.

He let slip that he was worried enough about his health to have a heart-to-heart with his son, Jordan.

“Not many things scare me, but I was concerned,” he said.

Sources told The Post that Adams had complained about a lingering pain in his side, which City Hall confirmed, before the New Year, as well as trouble getting around.

The troubles prompted doctors to conduct the colonoscopy in early January and a spate of additional tests, officials said.

As Adams awaited results and his pain lingered, he attended President Trump’s inauguration in Washington, DC – a last-minute and much-criticized trip that resulted in him being relegated to an overflow room with D-list celebrities.

City Hall officials said the colonoscopy turned up a result that spurred more tests and a doctor’s order for Adams to rest. The directive prompted a vague Jan. 26 statement from City Hall spokesperson Fabien Levy that Adams “hasn’t been feeling his best” and would be taking a break from his usual schedule.

Adams underwent an MRI, blood tests and a test for a bacterial infection in his gut that could cause stomach ulcers last week, which ended with a doctor clearing him Jan. 29, the officials said.

“All the tests came out negative,” Adams said.

“I had to go under for one of them … I was going to be under anesthesia,” Adams said Wednesday about the medical tests, apparently alluding to the Jan. 3 colonoscopy.

Adams also implied that at least some of his woes were related to his diabetes.

He said he’s 25 pounds heavier than his “true fighting weight” and will go back to a more plant-based diet, which he has credited for managing his diabetes.

Adams’ predecessors were much more quick to inform their millions of constituents about their health issues.

One day before Bill de Blasio underwent hernia surgery in 2015, his team told the public about the upcoming procedure and announced the then-mayor would return to City Hall within days. 

Former Mayor Rudy Giuliani in 2000 not only disclosed that he had 90 rice-sized radioactive titanium seeds placed in his prostate as a cancer treatment, but even held a news conference six hours later from the hospital. 

The secrecy by Adams is reminiscent of Michael Bloomberg, who stoked controversy by frequently taking sly weekend trips while mayor, especially to Bermuda.

Bloomberg was in Bermuda when a disastrous blizzard struck during 2010, raising questions about who was in charge during his absence.

One former Bloomberg aide also told The Post there’s reason to believe that the former mayor had a colonoscopy over his 12 years in office and never disclosed that routine medical procedure.

Adams contended an obscure executive order – which has been renewed since the Giuliani era – gave his first deputy mayor, Torres-Springer, power to act as mayor.

The assertion was quickly slapped down by Public Advocate Jumaane Williams, whose position is designated by the City Charter to take over if the mayor is incapacitated.

Williams said he wasn’t informed about Adams’ procedure, and the mayor broke the city’s rules.

“I am happy the mayor is feeling better – at the same time, I feel deeply disturbed by this latest evidence of the mayor ignoring city regulations to suit his own purposes,” Williams said in a statement. “He has long demonstrated a tendency to test how far he can go in bending or breaking rules, and this is a clear example.”

The City Charter states that the public advocate and then the city comptroller shall temporarily take over if the mayor cannot perform his duties because of sickness.

Adams argued the executive order supersedes the charter.

He renewed the order in September, clearing up the line of succession when his former First Deputy Mayor Sheena Wright’s future at City Hall was in doubt in the face of a spate of federal raids targeting top city officials close to the mayor.

Adams again quietly signed it Jan. 13, records show.

Williams said designating mayoral duties to Torres-Springer, who replaced Wright as Gov. Kathy Hochul directed the embattled Adams to clean house, does not replace the charter’s language on the continuity of government.

“Given the new disclosure of the mayor’s time under anesthesia last week, and his office’s failure to inform the public advocate of that fact at the time, it seems clear that this was a violation of the charter,” Williams said, including the incorrect date of the procedure that Adams gave.

“Failing to communicate in this case is irresponsible at best and deceptive at worst.”