Former Mayor Bill de Blasio was a troubled and ungrateful leader of the Big Apple, who would often go on “power trips” — putting his disdain for police officers on full display, according to one of the cops on his security detail.

Retired NYPD officer Katrina Brownlee dedicated nearly a fifth of her newly released memoir — “And Then Came the Blues” — to her years on the former mayor’s security detail, describing her complicated relationship with de Blasio, whom she labeled an egocentric and insecure public persona but a “genuinely caring person” in private.

“One thing that was always difficult for me to reconcile was de Blasio the man versus de Blasio the mayor,” Brownlee writes.

In one example, Brownlee skewered the mayor’s staff, packed with “white millennials” who talked trash about their boss while using the administration as a resume builder. But she also attacked de Blasio — who served from 2014 to 2021 — for not being grateful to New Yorkers for electing him to a second term.

“They would talk about him to me, saying, ‘He’s stupid. He doesn’t know what he’s doing. He’s not consistent. He doesn’t know how to run this city. He’s a disgrace,’” Brownlee dished of de Blasio’s staff.

“As much as I didn’t approve of the staffers’ nasty comments, I also didn’t feel sorry for the mayor,” she wrote. “He was incapable of managing his staff in a way that encouraged their growth or advancement and wasn’t remotely interested in creating new leaders.

“This pattern was evident at every level of his administration, and especially at the token holiday party he threw every year as a half-assed gesture of gratitude for the security detail. He would make a speech about how important we were and thank us for all we did for him, but the very next day he wouldn’t even say good morning.”

Brownlee also got the impression that the former mayor, who had a contentious relationship with the NYPD since the start of his administration, wasn’t too fond of cops.

“I also sensed that the mayor generally did not like police officers,” she wrote, adding, “Although he never disrespected me directly, he was so insecure about his own status that he couldn’t stand the thought of anyone else around him having power.”

“Once, when de Blasio was talking on the phone on the grounds of City Hall, a uniformed cop posted there briefly took off his hat, and de Blasio, on one of his typical power trips, took it as such a gesture of disrespect that he called the officer’s sergeant to complain,” she recalled in one of the only specific examples.

In the early days of de Blasio’s first term, hundreds of NYPD cops turned their backs on the mayor during a funeral for a pair of officers who were executed on the street, while union officials blamed de Blasio for the slaying.

During her time on the force, Brownlee started her mayoral security stint on First Lady Chirlane McCray’s detail before suddenly being removed with little explanation.

“All the [commanding officer] said was, ‘She doesn’t like you. It is what it is. If you don’t like it, you can leave,'” she recalled, without providing more details.

The 22-year vet said the dismissal from the detail left her fuming, and railed against McCray’s character and $1.25 billion boondoggle mental health initiative ThriveNYC.

McCray only wanted people around her who’d “respond with a smile and never offer her an opinion,” Brownlee wrote. She believed the city’s former first lady didn’t actually like to elevate strong black women like herself.

“Chirlane was a fraud to her core. … I was angry for months at myself and at the other New Yorkers who put Bill and Chirlane in office, because I felt like the whole city had been tricked.

“And, ironically, Black people in her camp—not just on her detail but her assistants and her staff— especially Black women, had seemed to disappear quickly.”

Brownlee, who wrote there had never previously been a black woman like herself assigned to a mayoral detail, recalled that de Blasio himself never displayed any racist behavior. 

But the former mayor’s personal openness didn’t shield Brownlee from experiencing racism on the job, particularly during a 2017 trip to Maine, where de Blasio was attending a women’s march.

Brownlee contended she saw “racism in real time” as she conducted a security sweep of a senior center, from a white Maine woman who her “up and down as if she had never seen a Black person before, and especially not one with any authority.”

Someone later called the senior center to complain that Brownlee was there to “case the joint,” as if she were about to commit a robbery.

“The same person then called de Blasio himself to complain about my presence, and that prompted the mayor to contact his inspector and demand that he get me out of Maine immediately,” Brownlee wrote. 

“Two white officers and one Black female officer went into a community center that was occupied by white people, and because someone didn’t like that, the Black woman got penalized. I was kicked off the trip without explanation, while the two white officers continued on to the mayor’s next stop, in DC.”

But Brownlee, who retired in 2021 as a first-grade detective, recalled a few stories of positive interactions with de Blasio, including the mayor giving her every Christmas off after telling him about her annual party while shopping together for the holiday.

“From then on, I was able to see some humanity in the mayor,” she wrote. “I realized he could be a genuinely caring person, someone I wouldn’t mind going out for wine with when I retired.”

De Blasio and Brownlee had a heartfelt farewell in his office, where she revealed she was writing a book.

The mayor at first appeared to believe it would be a tell-all about him, but Brownlee made clear it would be about her life, including being shot 10 times by her ex-fiancé.

“He didn’t speak for a long time. Finally, he asked me, ‘Why didn’t you ever say anything?’” Brownlee wrote.

“Because I knew I would be fired. Plus, there are some things you just can’t say.

“He just nodded. I knew he understood. Mayor Bill de Blasio was a rare politician in my eyes—both a considerate human and a politician who sometimes seemed to care only about what the next race would be or how he could run for office again. But all that mattered in that moment was for me to unburden myself and show my gratitude for the past eight years.”

The former mayor didn’t respond to a request for comment.