A 21-year-old autistic man died in the Brooklyn blaze that also claimed the life of firefighter Timothy Klein — with the resident’s stricken kin hailing the fallen Bravest as a hero to The Post on Monday.

Carlos Richards, who police sources said was the son of a retired NYPD cop, was reported missing by his family when flames broke out in their home on Avenue N near East 108th Street in Canarsie on Sunday afternoon, authorities said. 

Klein, 31, the son of a retired Bravest, died when the second floor caved in, officials said.

Several years ago, the fireman had given the eulogy for fellow firefighter Steven Pollard after Pollard was killed on duty at the scene of a Brooklyn car crash.

Later Sunday, Richards’ body was found in the home’s charred remains, authorities said. The young man was autistic and home alone at the time, said a woman answering a phone number listed for Richards’ mother. The woman declined further comment.

“Our condolences go to the family of the firefighter who died trying to save Carlos,” a man told The Post by phone Monday, after answering the same number.

“Our hearts go out to his family. Right now, we’re grieving for Carlos, and we share the same pain that they are feeling,’’ added the man, who did not identify himself.

On Monday, the dead man’s sister, Chloe Richards, posted a moving photo of her brother and mother on a GoFundMe page to help the family with funeral costs.

“The loss we are experiencing is monumental,” she wrote. “As we try to piece together all that’s happened, we’re raising money for Carlo’s funeral expenses so we can do right by our boy.

“He was such a bright light in our lives — he loved everyone and everyone loved him,” Chloe Richards said. 

She said donations will also help her mom “get back on her feet” after losing everything in the fire.

Chloe set a goal of $30,000 and had collected $5,530 in the first three hours the fundraising page was online. 

Fire officials say smoke-eaters were battling the blaze when flames suddenly swept through the second floor of the building, sending them leaping from windows as part of the structure began caving in on itself, fire officials said.

Klein — the  son of a retired fireman — was fatally injured in the structural collapse, according to authorities and sources.

Eight other firefighters also were injured, either in the collapse or from burns, officials said.

“Everything seemed to be going routine when suddenly the entire second floor became engulfed in flames,” Acting Chief of Department John Hodgens told reporters Sunday evening.

“Three other members that were with [Klein] were able to escape by jumping out windows and getting out ladders in other areas of the building.

“Our members worked feverishly, very hard under very difficult conditions, to try to reach [Klein],’’ Hodgens said. “Unfortunately, they were not able to get to him in time, and he succumbed to his injuries.

“Timothy lost his life doing his job that was asked of him every day.”

Mayor Eric Adams added, “It gives us great pain and sorrow to announce that New York City has lost one of its bravest, Timothy Klein, 6 1/2 years as a firefighter, 31-years-old, coming from a rich tradition of dad and other relatives who are firefighters.

“New York has lost one of its Bravest.”

Klein grew up in Breezy Point, Queens, and lived in Rockaway, sources said. He is survived by his father, retired FDNY Firefighter Patrick Klein, his mother Diane and his three sisters, according to officials.