State Assembly Speaker Carl Heastie — one of New York’s most powerful Democrats — is expected to back socialist Zohran Mamdani’s mayoral bid after Gov. Kathy Hochul’s shock endorsement, The Post has learned.

The influential Bronx Dem’s endorsement of the Queens assemblyman is “imminent,” a source close to Heastie’s and Mamdani’s camps said Tuesday.

Heastie is one of the last remaining New York Democratic establishment holdouts who has yet to back Mamdani, along with House Minority Leader Hakeem Jeffries, Senate Minority Leader Chuck Schumer and Sen. Kisten Gillibrand.

His endorsement would follow Hochul’s announcement Sunday evening that she was backing the lefty Democratic nominee. 

Another assemblymember also confirmed the speaker’s endorsement of Mamdani was in the works.

Heastie’s office didn’t return a request for comment.

The speaker has remained surprisingly silent as other local Dems have jumped on the Mamdani bandwagon, including the leader of the Bronx Democratic Party, state Sen. Jamaal Bailey just earlier this month.

Heastie was noticeably absent from the Bronx Dems’ endorsement announcement. Mamdani said at the time that the speaker was recovering from surgery and was unable to make it.

“I’ve appreciated the relationship that we’ve had while we’ve been in the assembly and even through this process,” Mamdani said.

But Heastie and the two-term assemblyman have had a touchy relationship in the past.

For instance, Heastie killed a free bus program in Queens pushed by Mamdani as part of the state budget last year after the socialist pol refused to vote in favor of the spending package.

Behind closed doors, the speaker has also consistently directed his ire towards Mamdani’s Democratic Socialists of America pals, both over their actions in his chamber and on the campaign trail.

The DSA challenged three incumbent Democrats in New York City last year, unseating one of them, all with Mamdani’s endorsements.

Claire Valdez successfully took on Assemblyman Juan Ardilla in Queens, while Eon Huntley saw a challenge to Assemblywoman Stefani Zinerman fail in Brooklyn. Jonathan Soto also unsuccessfully primaried Assemblyman Michael Benedetto in The Bronx.

Despite the open animosity on the campaign trail, Heastie has dismissed the concern about left-wing primary challenges.

“I would say that probably 80% of the stuff that Zohran has campaigned on, the Assembly Democrats have supported,” Heastie told reporters in Albany last month.

Sources familiar with the speaker’s thinking said he floated the idea of whether or not he should endorse Mamdani to members over the last few months.

Soon after Mamdani won the Democratic mayoral primary in June, Heastie told him to mend fences with his Assembly colleagues if he wanted to earn the speaker’s endorsement.

Benedetto said he understood why Heastie would support the Democratic nominee, but he told The Post endorsing Mamdani is “a bit of a stretch for me.”