Top prober now facing down ex-pal de Blasio

He was once Mayor de Blasio’s close pal and campaign treasurer — but now the city’s Department of Investigation chief has become an archenemy.

One possible reason: Sources say he’s positioning himself to run for public office as a fearless investigator unafraid to take on the powerful.

Commissioner Mark Peters befriended de Blasio in the 1990s, when both were serving on the school board in Park Slope.

The former prosecutor served as de Blasio’s campaign treasurer in 2013, donating more than $7,000 to the mayor’s election effort.

But, mulling his own run for public office, Peters has proved he isn’t afraid to butt heads with his boss.

Last week, Peters’ agency issued a blistering report on a slew of Correction officials, including Commis- sioner Joseph Ponte, who misused their city vehicles for personal purposes.

Despite the damning findings, de Blasio was quick to defend Ponte — prompting Peters, in an extraordinary move, to issue a scathing retort.

“There can be no defense of this behavior, and City Hall harms government integrity by even trying,” Peters said.

Arnold Kriss, a politically connected lawyer who regularly deals with DOI, said Peters was making a statement with his latest report since “normal procedure” would have been to refer the agency’s findings to the Conflicts of Interest Board before announcing them.

“What Peters did is contrary to the way COIB matters are handled,” Kriss said. “He obviously wanted to show he’s independent of de Blasio.”

Sources say Peters is in- terested in making a second bid for Brooklyn district attorney in four years, depending on how the race shakes out this year, and is also considering a run for state attorney general if Eric Schneiderman makes a bid for governor.

DOI issued a statement Tuesday night saying Peters intends to serve in his post “for a long time.”