Cops say a brooding boyfriend fatally stabbed an au pair and her boss — a popular Manhattan comedy-club owner — in a quaint suburban New Jersey town over the weekend.

“Oh, my God! Oh, my God! Oh, my God!’’ a neighbor said she heard a woman scream from the Maplewood home early Saturday.

Killed in the carnage were The Stand owner David Kimowitz, a 40-year-old married dad of two, and the family’s Colombian au pair, Karen Bermudez-Rodriguez, 26.

Kimowitz’s wife and two pre-school-age daughters are believed to have been spending the weekend at the Jersey Shore at the time.

Neighbors said Sunday that the nanny’s boyfriend, 27-year-old Joseph Porter of Elizabeth, NJ, appeared to be stalking her in the days leading up to the double homicide — including the day right before the slayings.

“The boyfriend was sitting parked here in a dark Toyota Corolla all day Friday. The other neighbors took notice. There was a little something off there,’’ said Kathy Cantwell, 63, who lives next door to the Kimowitzes on Walton Road in the leafy Essex County enclave.

Residents said Porter got out of his car a few times, but only to pace up and down the street. At one point that night, during a party that his girlfriend threw for other nannies at the home, he stood in some nearby woods, they said.

“The relationship went south, and he was kinda stalking her,’’ a neighbor said of the accused killer and his girlfriend. On Friday, “My neighbor called his son and told him to keep the doors locked because he didn’t like the looks of this guy.”

Hours later, all hell broke loose.

“I sleep with my windows open. At 6 a.m., I heard it. It was piercing. Blood-curdling screams over and over,’’ Cantwell said.

She said a woman outside the home kept screaming, “’ Oh, my God!’

“Repeated over a dozen times. Over and over for several minutes,’’ Cantwell said. “Whoever it was, she was in shock.’’

Another resident, Andrew de la Torre, added to tapinto.net, “There was a repetitive scream that sounded like someone saying, ‘No! No! No!”

A 20-year-old jogger who happened to be running by the nearly million-dollar house saw the bloodied nanny lying in front and tried to help her as she called the police, neighbors said.

The au pair was pronounced dead within the hour at the hospital. Kimowitz was found dead inside the home.

Porter was nabbed in Newark, NJ, hours later and charged with two counts of murder and weapons possession, authorities said. The motive for the killings was not immediately clear.

His girlfriend had been working for the family for about a year, after coming to the States to learn English, a pal told NJ.com.

The beloved Kimowitz was well-known on the comedy circuit. His Union Square club has drawn the likes of Tracy Morgan, David Chappelle and Damon Wayans.

On Saturday, Kimowitz’s “brother was sitting right there in front of that tree with his head in hands, rocking,’’ said a neighbor, standing near the home. “He was in shock. The only thing he kept saying was, ‘My brother lives there, my brother lives there.’ ”

At the comedy club Sunday, a distraught-looking man arrived on a bicycle in the afternoon and only said, “Yeah, it’s crazy,’’ before ducking inside. The club’s shows are canceled through at least Monday night, said one of Kimowitz’s partners.

“This is such shocking news. A great guy and friend has passed this weekend. Just talked with him last week and Fri night. He seemed so happy, a wife, 2 kids, his new club opened. And now this horrific new. David Kimowitz you will be missed. RIP’’ comic Rich Vos wrote on Twitter.

Residents said Kimowitz and his wife had moved with their kids to Maplewood fewer than two years ago to escape the grind of the city, spending a year and a half renovating the gorgeous home.

“They moved from Manhattan. That was a big deal for them,’’ Cantwell said. “He and his wife had just had their second baby. She’s pushing 2 now. The older one is 4.

“They really built that house together,’’ she said of the Walton Road home. “They redid everything. The entire place needed to be gutted.’’

“David was a very nice neighbor,’’ she said sadly. “They bought a snow machine last year, and he snowplowed my sidewalks for me.”

-Additional reporting by Khristina Narizhnaya