With horrified family members crying out in anguish, a Brooklyn man and his adult son died together of a double opioid overdose while celebrating a family birthday party Sunday, police said.

Joseph Andrade, 44, and his 22-year-old son, Carlos, lost their lives soon after excusing themselves from the festivities by telling people they were going for a smoke.

For some reason, the younger man, who was not known to use drugs, joined his father, a reputed addict, in taking some powerful opiates — apparently snorting a mix of heroin and fentanyl, police sources said.

Carlos — his face turning purple as he asphyxiated — was discovered by his girlfriend, Jasmin Santos, just inside the foyer of his father’s building just after 3 a.m.

“Jasmin found Carlos dying,” a cousin, Sonia Santos, told The Post. “She screamed and tried to help him. She said he was turning blue.”

Joseph was found feet away, outside the building on 27th Street near Fourth Avenue in Greenwood, according to cops.

The distraught women called 911 and responding officers administered Narcan, a drug that reverses the effects of an overdose. But it was too late, and both men died at Lutheran Medical, authorities said.

Carlos had driven up from Maryland for the birthday bash with Jasmin and their children, ages 1 and 4, a relative said.

“He was very close with his oldest son,” Santos said of Carlos. “I don’t know what they are going to do without him.”

Acquaintances said Joseph, who worked on and off as a mechanic, may have struggled with addiction.

“The father had a problem,” said a neighbor who asked that their name be withheld. “People knew. I was surprised Carlos was involved. He was a good son.”

“That building was always fine until recently,” another resident lamented. “We’ve never had anything like this before, but lately there’s been a lot of men, drinking, getting drunk outside, late into the night.”

The father and son’s deaths are under investigation and the cause will be determined by the medical examiner, officials said. A projected total of 1,300 people are believed to have succumbed to drugs in 2016, officials have said.

Additional reporting by Emily Saul