A prominent New Jersey doctor well known for taking in foster kids was rocked by an unthinkable horror — when one of his adopted children ­allegedly stabbed another to death in their home.

“Rest peacefully, angel,” Dr. Robert Gallo wrote on his Facebook page with a picture of his daughter Teia, 20.

Her foster brother, Travis Gallo, 17, allegedly stabbed her repeatedly with a kitchen knife at around 5:30 p.m. Thursday in front of two other siblings at their Washington Township home, sources said.

Their brother called 911, while another sister fled the home with no shoes on, sources said.

“You could hear people screaming,” a neighbor said. “It was a nightmare.”

Teia and Travis had both been adopted by Gallo, an OB-GYN, as children. The patriarch also adopted Teia’s biological sister, Destiny, and has nine kids of his own.

The physician told The Post he was at a loss to explain the tragedy that stunned his tranquil suburban neighborhood.

“He snapped,” Gallo said. “We still have a lot of unanswered questions.”

Travis Gallo was arrested at the scene and pleaded not guilty to murder as a juvenile in a Hackensack court Friday afternoon, officials said.

Prosecutors may still charge him as an adult for the slaying.

Teia’s sister, Destiny Gallo, grieved with her father on his Facebook page in a heart-wrenching post on Friday.

“She was so beautiful daddy,” she wrote of the Paramus Catholic HS graduate and Dominican College student. “She walked in your footsteps. You were her inspiration without a doubt and she loved you.”

Dr. Gallo said the family will help one another through the grief.

“We’re pretty strong people,” he said. “There’s a lot of love in this family. We’ll get through this.”

Sources said that Travis Gallo frequently fought with his sister and that the disputes sometimes turned violent.

The big-hearted doctor took Travis in at age 3 for what was supposed to be a temporary arrangement until he could find the tot a permanent home.

But Gallo grew attached to the boy and decided to keep him permanently.

“After you have them in your house for a year and they call you Mommy and Daddy, it’s very difficult to turn them away,” he said.

Teia, who friends said had a boyfriend in the Army, was brought into the expanding household at age 4 with her sister.

A trove of pictures on Dr. Gallo’s Facebook page shows the grinning clan vacationing everywhere from Southern California to Bermuda to Manhattan’s Little Italy.

“They are just a beautiful family, very kind, very decent,” a neighbor said. “This is all just shocking.”

One set of photos taken the day before the murder, on Christmas, shows Teia smiling broadly with her siblings.