Zohran Mamdani will not be sworn in as New York's 111th mayor after surprising revelation comes to light

According to the research, Mayor Matthias Nicolls served a second, nonconsecutive term that isn’t accurately reported in the official record.

Another historian and a historical group affirmed the findings, reports The Gothamist.

The new revelation would mean the number of every subsequent mayor is off by one. Current mayor Eric Adams, who often makes the declaration "I’m 110," would actually be 111.

Mr Hortenstine said he first made the discovery while researching the ties between early New York City mayors and slavery.

He found references to Nicolls’ second term in an archive of papers of Edmund Andros, the colonial governor of New York.

The public policy and history writer who lives in Washington DC has now called on the mayor's office to make an official correction.

Nonconsecutive terms for mayor are counted twice, mirroring the system used for US Presidents.

Mayor Nicolls’ first one-year term in 1672 is recorded in a book of mayors at the municipal archives, "The Renascence of City Hall."

He told The Gothamist: "This was in 1675. So then, when I later looked through the official list of the city, I noticed that they had missed this term."

Other documents, including materials at the New York Historical, were found by Mr Hortenstine also make reference to Nicolls' second term.

A spokesman for the New York Historical, said a preliminary search of the museum’s archives found three references to Nicolls’ 1674-1675 mayoralty in "The Iconography of Manhattan Island."

The book is a history of New York based on primary sources and seems to confirm Mr Hortenstine's theory.

Further research revealed historian Peter R. Christoph had made a similar revelation in 1989 in his essay "Record of the New York Genealogical and Biographical Society."

He wrote: "Edward I. Koch is the 105th Mayor of New York. The City Of New York Official Directory says so. So does The New York Times. But they are wrong: He is the 106th.

"Not only is he misnumbered, but so is everyone else after Mayor No. Seven. It is a mind-boggling thought: 99 mayors misnumbered, most of them gone to the grave, secure in the knowledge of their place in history, but all of them numerically out of whack. How could such a thing happen?"

The historian's revelation came from a footnote that the error appeared in an 1841 Manual of the Corporation of the City of New York.

It was transcribed into later documents and was never rectified. Mr Christoph, who worked for the New York State Library, died in 2019.

Assistant commissioner of the city’s Department of Records Ken Cobb said he knew of no effort to investigate the mistake.

He said while he could not find any mention of Nicolls’ second term, he did not dispute Mr Hortenstine’s findings.

Mr Cobb said: "We're the keepers of the records. We're not the creators of the records. It's a good question. Who noticed this discrepancy? Apparently, this historian did."

It's not the first time the official list of mayors has been corrected. In 1937, Charles Lodwick, who served from 1694-1695, was inserted retroactively as the 21st mayor.

Mr Cobb added: "Everyone jumped up a number and that's been the way ever since."

Randy Mastro, the first Deputy Mayor, said he had never heard of the missing mayor, adding: "I think we will leave this issue for historians and, for a change, the next administration."