NYPD Commissioner Keechant Sewell announced her resignation on Monday, a decision that left many within the nation’s largest police department shocked.

The move came after Sewell met with New York City Mayor Eric Adams at City Hall on Monday afternoon.

She announced her sudden resignation in a letter addressed to her fellow colleagues.

“Since I joined you almost a year and a half ago we have faced tremendous tragedy, challenges and triumphs together. I have witnessed your compassion, heroics and selflessness on a daily basis. They have reaffirmed to me, what people around the globe have always known: you are an extraordinary collective of hard working public servants dedicated to the safety of this city, engaging our communities and sharing what we know with our partners for the benefit of the world. You and your predecessors are the reason that the NYPD is known as the gold standard in law enforcement. I have had the absolute honor to spend time with our line of duty families. Their loss is immeasurable; their strength is incredible. I thank them for allowing me the privilege to know them and hear the stories of our fallen heroes.”

Mayor Adams released a statement following the announcement.

“I want to thank Police Commissioner Sewell for her devotion over the last 18 months and her steadfast leadership,” Adams said. “Her efforts played a leading role in this administration’s tireless work to make New York City safer. When we came into office, crime was trending upwards, and thanks to the brave men and women of the NYPD, most of the major crime categories are now down. The commissioner worked nearly 24 hours a day, seven days a week for a year and a half, and we are all grateful for her service. New Yorkers owe her a debt of gratitude.”

I want to thank Police Commissioner Sewell for her devotion over the last 18 months and her steadfast leadership. Her efforts played a leading role in this administration’s tireless work to make New York City safer.

— Mayor Eric Adams (@NYCMayor) June 12, 2023

The mayor was said to be surprised by the news, but for months, tension has been brewing.

The tension appeared to surface in public last November when Sewell gave a speech to a banquet for fellow policewomen.

“Understand you will be second guessed, told what you should say, told what you should write, by some with half your experience,” Sewell said at the banquet. “You will get free, unsolicited personal advice. Your hairstyle is wrong, you look tired, already worn out in less than a year.’

Sewell’s resignation comes about a year and a half after she became the first woman to lead the nation’s largest police department when she was sworn in on January 1, 2022.

The mayor selected her after an exhaustive nationwide search, during which he vowed to name the first female police commissioner in the NYPD’s history.

He picked her despite several large city police chiefs rumored to be in the running. Sewell had previously been Nassau County’s chief of detectives, in a department that had about 2,400 total uniformed officers.

Sewell faced difficult challenges during her tenure, including a first month in office that saw five NYPD officers shot in January of 2022.

Under her leadership, the Queens native oversaw a drop in index crime and deployed new so-called neighborhood safety teams.

As of June 11, crime was up this year by only .92%. Meanwhile, murders were down 12.5%, rape down 9.5%, transit crime down 7.9% and shootings were down 25%.

Sewell won the respect of the rank and file by trying to install fairer and more consistent discipline for officers. She also negotiated a groundbreaking union agreement giving officers historic raises.

Both the heads of the Police Benevolent Association and Detectives’ Endowment Association lauded Sewell’s impact.

“In her short time with the NYPD, Commissioner Sewell made a real impact,” PBA President Pat Lynch said. “She took over a police department in crisis and faced tremendous challenges from day one. She cared about the cops on the street and was always open to working with us to improve their lives and working conditions. There are still enormous challenges facing the NYPD. Her leadership will be sorely missed.”

“The DEA salutes Commissioner Sewell for leading the NYPD through some of the most tragic and difficult times in the department’s history,” Detectives’ Endowment Association President Paul DiGiacomo said. “Her love of detectives was genuine and sincere — and her support of the union never wavered. Commissioner Sewell’s historic appointment will not soon be forgotten.”

But still, sources cited increasing tension with City Hall, which 30-year NYPD veteran Mike Alcazar said is nothing new.

“I’ve seen this happen with police commissioners where the mayor really runs the show,” he said. “We saw this with de Blasio. With summer coming, historically crime is going to spike and if she can’t do her job, she’s just going to step down.”

It’s not yet clear why Sewell decided to step down.