A retired NYPD K-9 is barking back to active duty — marking a historic first for Gotham’s elite four-legged crimefighters.

Mahmoud, an 8-year-old Belgian Malinois, had been enjoying retirement for about two months until his NYPD handler, Detective Kirk Boone, died of natural causes in July shortly after retiring, according to officials.

NYPD dogs usually retire with their handlers because they’ve worked and lived together for so long.

But Boone’s family thought returning the pooch to service would be a way to honor the detective, said Detective Jeremy Lucca, Mahmoud’s new handler.

“Unfortunately, he passed away and his dog obviously retired with him,” Lucca said. “But to honor that and to honor his legacy, the family thought it would be most fitting to have his dog come out of retirement and continue the service.” 

“It’s an absolute honor to carry on a part of Kirk Boone and also Officer Mahmoud with K9 Mahmoud,” Lucca said. 

Mahmoud — who is named after Boone’s prior human partner in the 75th Precinct, Officer David Mahmoud, who died of 9/11-related cancer in 2010 — was assigned to Lucca in August and has been receiving training to bring him back up to ‘sniff.’

“We’re just finishing up a search and rescue program where they’ll be certifying, hopefully, next week,” he said Thursday, explaining that the dog is learning new tricks.

And he’s been hard at work since his return, fetching overtime details around the city, Lucca said.

“We helped cover the US Open, the United Nations General Assembly,” he said. “We have some details coming up the rest of the year. And yeah, we’re going to still hone his skills and work together and hopefully get certified in a couple of the specialties.” 

Mahmoud is also a trained cadaver- and drug-sniffing dog, Lucca said, adding that he’d known Mahmoud during the dog’s time with Boone, who had been his friend.

“So I knew his characteristics,” Lucca said. “I just didn’t know exactly how he works and operates – just from hearing what Kirk Boone would talk about. So we’re learning and growing together.

Mahmoud, an energetic dog who’s curious and friendly, was only out of service for a couple months so it was an easy transition to return to the Finest, lead ESU K9 trainer Det. Scott Mateyaschuk said.

“It brings back the legacy of Kirk Boone, and he was just a great guy all around,” Mateyaschuk said. 

Boone was a 75th Precinct cop — covering East New York, Brooklyn — prior to joining ESU, and David Mahmoud was his partner.

“And so it’s a round circle here having all these things connect, and it’s been a real inspiration to guys here as well, because Kirk was such a mentor to everybody,” he said. 

“We see him in another two years of service, and then we’ll retire him at 10 years old,” Mateyaschuk said, adding that 10 is the average retirement age for NYPD pooches.

The Detectives Endowment Association called Mahmoud and Boone “selfless heroes.”

“It’s an amazing way to carry Kirk and David’s legacies forward,” DEA president Scott Munro said.

Lucca expects to be with Mahmoud for a long time.

“I’ll have about a year left before I hit 20 years,” Lucca said. “So if I do leave at 20, he’s going to be retiring with me.”

At that point, Mahmoud will finally be able to live a dog’s life, Mateyaschuk said.

“Dogs just hanging around, you know, and not coming to work, not jumping in and out of cars, not on perp searches, not any of this stuff,” Mateyaschuk said. “The stressful life they lead … They’ll probably just hang out in the backyard and, you know, be a dog.”