Michael Bloomberg, former Mayor of New York City, speaks at CityLab Detroit, a global city summit, on October 29, 2018 in Detroit, Michigan.

Real estate makes strange bedfellows.

Mike Bloomberg, the 2020 candidate who is using his personal fortune to try to defeat President Donald Trump on Election Day, owns a condo in a Trump-managed property, Crain's New York Business reported.

The billionaire bought a unit in one of the Trump Organization's developments for $3.8 million in late 2000, just as he was preparing for his first run for mayor of New York.

The value of the apartment at 610 Park Avenue in Manhattan is now close to $6.2 million, according to Crain's.

Neither the Trump Organization nor a Bloomberg campaign representative returned a request for comment from CNBC.

Bloomberg entered the 2020 Democratic race in November, arguing that he would do the best job of competing with and beating Trump.