The father of the alleged teen gunman who killed four people in a mass shooting at Apalachee High School in northern Georgia has been arrested, law enforcement officials announced Thursday night.

Colin Gray, 54, was charged with four counts of manslaughter, two counts of second-degree murder and eight counts of cruelty to children, the Georgia Bureau of Investigation said the day after his 14-year-old son Colt Gray was charged with murder.

The charges come after it was revealed that Colin Gray purchased the AR-15-style rifle Colt allegedly used in the massacre as a Christmas gift last December, sources told The Post.

“These charges stem from Mr. Gray knowingly allowing his son, Colt, to possess a weapon,” GBI Director Chris Hosey told reporters at a press conference, without providing any additional details.

Colt received the deadly present from his father just seven months after authorities visited the pair when the FBI received tips about online school shooting threats, according to the federal agency.

The disturbing online posts reviewed by law enforcement included photos of guns.

Colin Gray told police at the time he had hunting guns in the home — but said Colt did not have unsupervised access to them, according to authorities. 

The teen also denied making the threats.

Colt Gray allegedly gunned down two fellow students and two teachers when he opened fire at the school on Wednesday morning.

Those killed were students Mason Schermerhorn and Christian Angulo, both 14, and math teachers Richard “Ricky” Aspinwall, 39, and Christina Irimie, 53. Aspinwall was also an assistant football coach.

Nine others — seven students and two teachers — were hospitalized with gunshot wounds.

Barrow County Sheriff Jud Smith said Thursday night he was happy to reveal that all of those injured “will make a full recovery,” with some victims already released from the hospital.

“We met with them today. Emotions are very high, obviously, but we told them that we love them. We love our teachers and what they do, and we’re very happy at the fact that they stood in the gap between evil to protect their children,” Smith said.

Colt, who surrendered to school resource officers immediately, was initially charged with murder on Wednesday — but as of Thursday is now facing four total counts of felony murder, Hosey announced.

“We will continue to work tirelessly to complete this investigation as we move forward,” he said, adding that they have “a long way to go before it’s finished.”

The disturbed teenager came from a broken home, where he and his sister were regularly abused by their troubled mother and visited frequently by police and child services, a former neighbor and landlord told The Post Thursday.

Colt’s mother, 43-year-old Marcee Gray, 43, has a lengthy rap sheet spanning 17 years and four Georgia counties, including arrests for drug possession, driving under the influence and domestic violence.

Lauren Vickers, who lived next door to the Grays in Jefferson, Ga., said the children were always wearing dirty clothes and sometimes were hungry.

“It was constant abuse,” she said.

Colt’s aunt, Annie Brown, told the Washington Post that her nephew was struggling with mental health issues, and had been “begging for help from everybody around him,” before he shot up the school.