A Brooklyn woman has filed a lawsuit after a terrible hospital mix-up left her grieving the death of a man she thought was her brother, but who was actually a stranger.

In July, a man named Freddy Clarence Williams was admitted to St. Barnabas Hospital unconscious from an apparent drug overdose. Although Williams had a Social Security card that had his full name on it, doctors still called Shirell Powell and said her brother was brain dead, reported the New York Post.

Although Powell’s brother is also a 40-year-old named Frederick Williams, he does not have a middle name.

“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 immediately went to the man’s bedside and began prepping for the worst possible outcome.

“That is my baby brother, so it was really hurtful,” she said. “I was worried, hurt, crying, screaming, calling everybody. It was a horrible feeling.”

Eventually, Powell called her relatives down South to come to New York and say their goodbyes. When Powell’s sister came to see the man, she questioned if it was really their brother.

“She walked up into the room and said, ‘That is not my brother,’” Powell recalled. “I said, ‘What do you mean?’”

“The guy was much bigger,’’ Powell explained.

However, after a closer look, Powell’s sister agreed the man resembled their brother.

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

Then came time for the body to undergo an autopsy. After the Medical Examiner’s Office revealed their findings, Powell and her family learned the truth: that was not their brother.

“I nearly fainted because I killed somebody that I didn’t even know. I gave consent,” said Powell.

As it turned out, Powell’s actual brother was in jail on a July 1 assault arrest in Lower Manhattan.

After seeing her brother in court and speaking with him at Rikers Island, Powell tried to find a way to contact the actual victim’s family.

“The representatives [at St. Barnabas] basically spit in my face,” Powell’s lawyer, Alexander M. Dudelson, said referring to his attempt to get information on Freddy Clarence Williams. “This is beyond reckless conduct. I requested an investigation. Nothing more. An apology would have been nice.”

Powell also asked the Medical Examiner’s Office for the dead man’s family information so she could send condolences, but it denied the request, citing privacy concerns.

Now, Powell is unable to sleep, thinking about the man’s family.

“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."

“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,” she told The Post.