A gunman fatally shot his elderly mother, his daughter and his daughter’s boyfriend inside the doomed family’s Bronx NYCHA apartment and then took his own life Wednesday morning, police source said.

The 44-year-old shooter called an out-of-state relative and said, “Check on your family,” according to a police source.

That relative called a local family friend, who went to the apartment in the Castle Hill Houses on Lacombe Ave. near Castle Hill Ave. about 9:40 a.m. and cops were called.

Inside, they discovered the shooter dead on the couch with the murder weapon still in his hand, police sources. His 26-year-old daughter was dead in the rear of the home along with his 75-year-old mother, the sources said. The daughter’s boyfriend, believed to be in his 20s, was dead near the apartment’s door.

The shooter’s and victims’ names were not immediately released.

Henry Tucker, 60, lives in the building and has known the family all his life. He identified the slain family matriarch at Theresa Stukes, who just celebrated her birthday on Oct. 30.

“We grew up with each other,” he said. “I loved her family. Obviously, it’s devastating what happened to her and her family … She watched me grew up. I watched her age well. Her family is like my family. Her children, her grandchildren, we had a genuine love for each other. A wonderful woman”

“I’m like everyone else, in shock,” he added. “She did not deserve this. Her family did not deserve this. She just celebrated her birthday a few days ago … It’s just tragic all around.”

Tucker has known’s the gunman’s slain daughter since she was born. He said she was a health care worker.

“She was very quiet, always respectful,” he said. “Just went about her business. Very kind and gentle. She was definitely a sweetheart. Nothing negative i could say about her, from birth.”

Tucker even had a good relationship with the gunman.

“Maybe a month ago, I saw him coming in and out of the building,” he said. “He was coming to see his mom. I was on my way home. We extended hand shakes and hugs: ‘Love you, brother,’ ‘Love you too,’ things of that nature. If anything was going on, he put on a good front. That’s definitely what’s making it even more troubling. I just never got the feeling that he was headed down this path.”

The gunman did a stint in prison when he was younger, Tucker said.

He turned his life around, or it appeared that way,” Tucker said. “”He was doing well, working, taking care of himself … I never had any signs that he was off the deep end. if anything, if that was the case, it had to have just happened.”

“I didn’t get any negative vibes from him whatsoever,” he added. “That’s why it’s shocking to me.”

The slain matriarch has another daughter, who was not in the apartment when the murder-suicide happened, Tucker said.

“She was obviously in shambles,” Tucker said of that daughter learning what had happened. “You can only imagine how she’s feeling.”

Jeannette Martinez, 48, said she was “heartbroken” when she found out about the incident after a NYCHA worker cleaning the building broke the news to her, later discovering Theresa was one of the victims.

“Miss Theresa was a wonderful, wonderful person. She always been out doing celebrations, special occasions, barbeque, supporting people, giving good advice, and all that,” Martinez said. “I started crying [as soon as I heard the news] because that’s one of The Golden Girls. I call her Golden Girl, ’cause I got respect for older people.”

Luis Rolan, who lived in the building, said Theresa was a “very energetic” person who would always greet him and his daughters in the morning.

“Fantastic, wonderful lady. I just spoke to her last week. Last interaction… very energized. [She] always had a positive, smiling face,” Rolan said. “I just found of this morning. It’s devastating to hear about it.”

With Kerry Burke and Nicholas Williams