The off-duty NYPD officer killed in a one-car crash on the FDR Drive is a 25-year-old Brooklyn cop who dreamed of one day becoming a detective, sources told The Post on Saturday.

Officer Garman Chen, who works out of the 76th Precinct in Carroll Gardens, was driving north on the busy highway near 23rd Street at about 2:30 a.m. when he lost control of his black Lexus and smashed into a barrier pole supporting a pedestrian footbridge, police and sources said.

The Midwood High School graduate had three years on the job and was taken to Bellevue Hospital, where he was pronounced dead.

“I still can’t believe the news and I’m still shaking from the phone call. Rest in Peace to my brother Garman. From High School, to Cadets to Brothers in Blue,” his friend Robert Lee wrote in a Facebook post.

“Whether it was hanging out in [high school], waking up mad early to go to monthly training, passing around your study guides for the academy because you were the first to go in, or both dreaming about being detectives, I knew at the end of the day you had my back and I had yours.”

Two other passengers were injured in the fiery crash — an FDNY firefighter who suffered body trauma and a woman whose right foot was severed, officials said.

Both were taken to Bellevue and were listed in stable condition, police said.

Chen’s childhood friend Steven Grant told The Post that the rookie cop was always there for him — “no questions asked.”

“He was the best friend anyone could ever ask for. Whenever I needed him, he was there, he said, adding that the pair had known each other since attending P.S. 217 elementary together.

“I went to the hospital to confirm it wasn’t him…I didn’t want it to be him. I was like no, this isn’t Garman. This isn’t happening,” Grant’s sister told The Post.

Chen was part of the Grant family, she said, spending every holiday with them.

“He was selfless… a great person all around. Always helping everyone he sees — I mean, he’s a cop, right?” she added.

In September, Chen helped rescue a puppy found in Red Hook Park and return the pooch to his owner, a Facebook post from the precinct shows.

“Finally, it was the dogged efforts of Police Officers Chen and Gonzalez which made this a paw-fect day,” they wrote.