The chairman of the Bronx Democratic Party, state Assemblyman Marcos Crespo, will leave his powerful post this year, the lawmaker announced Friday.

Crespo said in a letter sent to supporters he would not seek reelection to his post in Albany, and sources told The Post the Bronx boss is also expected to step down from the leadership of the county party after the June 2020 primary elections.

“I was not happy,” said Assemblyman Jeff Dinowitz, a close ally of Crespo, of learning about his departure. “He’s a great assemblyman. It’s a loss to the Bronx and the whole state.”

The stunning move comes as his Bronx political machine has become one of the most powerful forces in state politics, thanks to the rise of Assembly Speaker Carl Heastie, who is also close to Crespo.

Crespo and his allies wielded great power in the Bronx, even handpicking the borough’s current district attorney, Darcel Clark.

She replaced Robert Johnson, who stepped down for a state Supreme Court seat.

Crespo’s decision injects even more uncertainty into Bronx politics just weeks after Borough President Ruben Diaz Jr. abandoned his 2021 Democratic primary campaign to replace Mayor Bill de Blasio, who is term-limited.

The Assemblyman was widely viewed in Albany as the frontrunner to replace Diaz. But now both have scotched their political ambitions — and launched new competitions to replace him.

Crespo was first elected to represent the borough in the Assembly in 2009 when the Bronx Democratic Party picked him as the nominee for a lightly contested special election to succeed Diaz Jr., who had been elected to the borough presidency.

He chairs the Assembly Labor Committee, which gives him clout over legislation affecting unions.

Bronx City Councilman and former state Sen. Ruben Diaz Sr. — who once employed Crespo as an aide — told The Post that Ken Burgos, the budget director in his office, will be running for Crespo’s seat.

“Ken is a smart guy. He knows the budget like the back of his hand,” gushed Diaz.

“I’m proud to promote youth.”

Diaz said Crespo is taking a job at Montefiore Medical Center.

Crespo did not respond to repeated requests for comment from The Post.

Additional reporting by Rich Calder