An image emerged on Thursday night of the teenager who chose his own birthday to open fire inside a Southern California high school, authorities said.

The 16-year-old — identified by CBS as Nathaniel Berhow — allegedly stormed into Saugus High School in Santa Clarita just before classes began Thursday, killed two students and injured at least three others with a .45-caliber semi-automatic pistol before turning the gun on himself, police said.

Berhow survived the self-inflicted gunshot wound to his head and is currently in “grave condition,” which means he is critical and clinging to life, at an area hospital, cops said.

He is a half-Japanese student whose family lives in Valencia, California, about two miles from the school.

One classmate described Berhow as a “quiet kid” to the Los Angeles Times.

“I would have never expected anything like this,” Brooke Hougo, 18, told the paper. “He was just a quiet kid.”

A photo of Berhow fits Hougo’s description — showing the baby-faced and shy-looking suspect smirking for the camera.

While a sophomore at Saugus, Berhow ran track and field for the school and competed in the 800-meter and 1600-meter races, according to stats on Athletic.net.

His father, Mark Berhow, died in December 2017 from a heart attack, but a “history of chronic alcoholism” contributed to his death, the Los Angeles County Coroner’s Office told The Post.

Two years before that, the father had been arrested during a domestic dispute with the boy’s mother.

In 2016, shortly before Mark Berhow died, the shooter’s mom sued him for custody of their children, according to records on Trellis.

“A quiet, to-himself kid,” said Ryan McCracken, a 20-year-old next-door neighbor.

When McCracken was younger, he said, they played together, sometimes in boy’s backyard tree house.

“You wouldn’t expect anything like that from him.”

With Post wires