Bloomberg was just gearing up for his first run for mayor when, the city Finance Department says, he bought the unit for $3.8 million from Esther Su of Singapore in late 2000. Documents show that he transferred the property to the Michael R. Bloomberg Revocable Trust in 2008. The trust acquired an on-site storage room from another tenant as his time at City Hall drew to a close in December 2013.

In 2016 the trust transferred the apartment and the storage room to a limited liability company, Park Avenue 5B. None of the transactions between Bloomberg, the trust or the LLC involved any exchange of money, and all three parties give as their address the offices of accounting and financial management firm Geller & Co., which has long handled Bloomberg's assets.

The Mayfair Hotel finished construction in 1925, with a design by architect James Carpenter. It has housed numerous New York City luminaries over the decades, including singer Luther Vandross and chef Daniel Boulud, who at one time ran the famed Le Cirque restaurant downstairs. Boulud now operates another French eatery, Daniel, on the premises.

Colony Capital—led by Trump associate and future inaugural committee chairman Thomas Barrack—purchased the Mayfair in 1997, and retained the future president to develop and manage the 15-story structure as a luxury condominium. The Trump Organization's website says all units sold out before the conversion was complete.

The organization did not immediately answer questions about what, if any, ownership stake it holds in the property or how much money it has invested in the building, which it continues to advertise and manage.

Details on Bloomberg's unit are scant. The listing website Trulia estimates its size at 2,202 square feet and its value as approaching $6.2 million.

The Bloomberg campaign did not immediately respond to requests for comment.