The contribution by Michael R. Bloomberg is the largest to a super PAC in the New York City mayor’s race this year and follows his endorsement of Andrew M. Cuomo for mayor.

Former Mayor Michael Bloomberg is prepared to endorse his old nemesis, Andrew Cuomo, for mayor Tuesday — backing an ex-governor who is mounting a comeback bid in the June 24 Democratic primary. Cuomo secured Bloomberg’s support after months of conversations between their top aides;