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, one of the cops on the mayor’s detail says.

Former 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 as an ego-centric but insecure public persona and as 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 usin

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