The “sister” of the Dayton, Ohio, shooter who was killed during the attack identified as a transgender guy — although his family had no idea, according to a report and some of his own social media posts.

Connor Betts’ 22-year-old sibling was named by authorities as Megan Betts in the days after the mass shooting, with cops releasing a statement saying relatives had lost “a daughter.”

But he apparently went by the name Jordan Cofer, and identified as a male, although he was only “out” to a small circle of friends, according to Splinter News, which spoke to several of those pals anonymously.

“Jordan was my closest friend,” one pal told the outlet. “He identified with he/him pronouns to people he trusted and knew would support him. Jordan was probably one of the sweetest people you would ever meet, a true saint, but he was also very scared constantly. He tried to give the best to everyone.”

One of his friends also confirmed to The Post: “I did know that he was indeed a trans man.”

On Sunday, the 24-year-old killer drove to a popular strip of bars and restaurants with Jordan — then made him one of the nine victims killed in the slaughter, officials said. Investigators have not yet identified his motive or whether his sibling was an intended target.

But his gender likely didn’t play a role in his death because Betts had no clue about his brother’s trans status, a friend told Splinter News.

“Jordan told me in the past that he was not out to his family, but that could have changed in the past month as we barely spoke of the topic recently,” said the friend. “I do not believe that his gender identity had played a part in his death because of the fact that he wasn’t out to many people.”

In a Tumblr account that also appears to be his, Jordan describes himself as an “ace poly trans boy with a loving heart and way too much work to do,” according to the outlet, which confirmed that the account was legit through a friend.

He also used the name Jordan on his Instagram and Twitter page, where he referred to himself at one point as a “guy.”

“I’m a Samsung guy but I just downloaded iTunes and got an Apple ID,” he wrote in an innocuous tweet to a pal in 2016.

Dayton police and several other friends of Jordan didn’t immediately return requests for comment Friday. But police said earlier this week they were not aware of his gender identity, according to Splinter News.