Imagine being told your brother is dying, and after two excruciating weeks you make the difficult decision to take him off life-support. Now imagine finding out that your brother is alive somewhere, and you just gave the order to kill a complete stranger.

That is exactly what Brooklyn resident Shirell Powell says happened to her last July. She claims in a lawsuit that on July 15, 2018, a 40-year-old man named Freddy Clarence Williams was admitted to St. Barnabas Hospital in the Bronx for an apparent drug overdose. The lawsuit, obtained by the New York Post, said that even though Williams had a social security card identifying him by his full name, the hospital called Powell because her brother, Frederick Williams (who has no middle name) was treated at some other time. Powell’s brother is also 40.

Powell went to the hospital to see her “brother.”

“He had tubes in his mouth, a neck brace,’’ Powell told The Post. “He was a little swollen . . . [But] he resembled my brother so much.”

She also said he couldn’t speak and was told after two days of testing that he was brain-dead and couldn’t recover. Powell called her relatives and told them the situation. When her sister arrived, she immediately rejected that the man in the hospital bed was their brother, but after closer inspection (and thinking their brother’s face was just swollen due to brain damage) she accepted the man as her brother.

On July 29, Powell “authorized [the hospital] to withdraw life support from Frederick Williams,” according to the lawsuit.

Powell’s nieces – Frederick’s daughters – took his death especially hard. Brooklyn, 17, came to New York from her home in Virginia to say goodbye to her father.

“She was hysterical,” Powell told the Post. “She was holding his hand, kissing him, crying.”

It wasn’t until the autopsy that the family discovered the man they just mourned was not their brother.

So where was their actual brother?

Frederick Williams had been in jail since July 1 after he was arrested for assault in lower Manhattan, hence why his family was able to believe he might be the man in the hospital.

Powell went to her brother’s hearing a few weeks after the ordeal to make sure he really was alive. She also spoke to him on the phone while he was at Rikers Island. He seemed at first dismayed by the fact that his sister was willing to pull the plug on him, but after it was explained there was nothing that could have been done for the man, he changed his mind.

“The doctors told her they couldn’t do anything,” he told the Post. “I’m not mad at her.”

Now Powell is suing St. Barnabas for what she and her family were put through. Hospital spokesman Steven Clark told the Post: “We don’t feel there is any merit to this claim.”

Powell and her attorney, Alexander M. Dudelson, tried to figure out who the man in the hospital was so they could contact his family, but the hospital has refused to give out that information due to privacy concerns.

“I barely sleep thinking about this all the time,’’ she told the Post.

“To actually stand over him and watch this man take his last breath — sometimes I can’t even talk about it because I get upset and start crying,” she said. “On the one hand, I’m thankful that it wasn’t [my brother]. On the other hand, I killed somebody that was a dad or a brother.”