A man going through a divorce stabbed his mother-in-law to death, wounded his teen brother-in-law — then slit his own wrists and set their Queens home on fire on Thursday, cops and sources said.

The 27-year-old man allegedly knifed his 50-year-old mother-in-law and her 17-year-old son multiple times inside a house on Smart Street near 45th Avenue in Flushing just before 4 p.m., authorities and sources said.

The man had been drinking before launching the assault on his in-laws, sources said. He then lit a mattress ablaze inside the home, sources added.

One of the victims ran outside the home screaming, catching the attention of a nearby Port Authority cop who rendered first aid and notified authorities, according to sources.  

The victims were taken to NewYork Presbyterian Hospital, where the gravely wounded mother-in-law succumbed to her injuries, and the teen, who was stabbed in the face and armpit, was listed in stable condition.

The alleged attacker was also hospitalized and placed in police custody, according to the sources.

A dozen FDNY and EMS personnel responded to the scene, with the flames knocked down by around 4:40 p.m., the department said.

Guqing Zhang, 20, and his sister Rouxin Lin, 16, were both in the basement of the home when they heard a bang and screaming – only to go upstairs and find their wounded, bleeding aunt and cousin.

“I was in a basement, playing games. 
We were in the basement when everything was happening,” said Zhang.

“I had my VR headset on, so I couldn’t really hear anything in the beginning. But then I heard loud yelling, and then they yelled quite a bit. So I came out to find out what exactly is happening,” he said.

“And that’s when I saw them…. [the 17-year-old] bloodied on the stairs and everyone was panicking… and I went to open the door and I went in (the room) and  I saw my aunt on the floor, not moving.”

“And then they said there was a guy with a knife inside,” Zhang added.

Lin also heard an “explosion” and went to follow her brother upstairs. 

“I smelled some smoke when I got to the stairs and I saw my cousin sitting on the staircase, bleeding, blood all over his body. That’s all I saw. After that, my brother just told me to go back downstairs. 
So I just stood downstairs until the police came,” Lin said. 

 “They were talking about a divorce. From what I’ve heard. I don’t know why. Like, everything was fine before. This is the first time this happened. 
I never heard any fighting upstairs. Never. It’s always calm,” said Lin. 

Lin said his slain aunt was a “really kind person” and a great cook. 

“I loved her cooking. Yeah, she made really good food. 
Like, once in a while, she comes down with a batch of food that she made. And it was really good,” she said. 

A resident of Smart Street for 65 years was also shocked to learn that the violent incident occurred on her otherwise quiet block.

“This is a quiet neighborhood.  The most trouble we have is the parking,” the woman, who wished not to be identified, told The Post. 

“I think the bad thing about it is that kids are messed up now. It’s like too much pressure on them,” she said.

 “It’s sad… I feel sorry for the family.”