A “beloved” Arizona teacher was decapitated and stabbed multiple times by her felon son before her relatives — who became concerned when she didn’t show up for her own surprise birthday party — made the disturbing discovery.

Teresa DeJesus Cruz Rubio’s headless body was found inside the Glendale apartment she shared with her 25-year-old son, Alejandro David Gonzalez, on Sept. 27.

The 49-year-old, a teacher at Southwest Key Programs, had been in contact with her sister throughout the day, confirming she would show up to a family gathering, which turned out to be her suprise party, according to the Glendale Police Department.

“The victim never showed up for the party, so the family became suspicious and went over to the house to try and get ahold of her to no avail,” Glendale police Sgt. Bryan Hoskin said at a press conference.

The family went to her home but couldn’t access the locked windows and doors and were forced to call a locksmith to help them get inside.

They made it into the home around 11:30 p.m., when they uncovered the horrifying scene.

Police found blood throughout the “small apartment,” the shower still running and a knife block in the kitchen sink with several knives.

“The victim suffered a full decapitation and had numerous stab wounds to her abdomen, chest and arms,” Hoskin said.

One of the knives had blood and hair on it, and it appeared that someone had attempted to wash it off, police said.

Cruz Rubio’s sister had loaned a burgundy GMC Yukon SUV to her, but the vehicle was nowhere to be found, she told police.

Gonzalez had been released from jail about 24 hours earlier after serving time for another felony, police said.

Cruz Rubio had picked up her son from jail and dropped him off at her home, according to AZCentral.

He is accused of stealing the SUV and fleeing.

Gonzalez reportedly had “mental conditions” and was capable of killing his mother, according to Hoskin and Fox 10 Phoenix, citing court records.

Video surveillance captured the suspected killer driving the truck westbound at 4:52 p.m. while Gonzalez contacted family members using his mom’s phone a half-hour later.

The SUV was reported as missing and Phoenix police discovered it near 99th Avenue and I-10 around 2:40 a.m. Sept. 28.

Gonzalez was spotted walking to and from the SUV several times before he was arrested 50 minutes later.

Police found Gonzalez had blood on his body and clothes and “injuries” to his hands and arms.

Gonzalez admitted to police that he stabbed his mother before claiming he cut her head off her body.

The suspected killer told police he had used methamphetamines and there was a second suspect.

He told investigators he had smoked methamphetamines with a black man who was biking in the neighborhood, the outlet reported, citing a police report. He said the man “did something to his mom” and then “had me stab her or something.”

Police have not found any evidence backing Gonzalez’s claim of a second suspect, but said the investigation is ongoing.

Gonzalez was charged with first-degree, premediated murder and felony theft of means of transportation.

He was booked into Maricopa County Jail on a $1 million, cash-only bond.

“It’s absolutely horrific,” Hoskin said. “It’s horrific to the family who had to endure this, it’s horrific to the officers who had to go and see this.”

“When you have a situation like this where an individual is capable of murdering his mother in such a heinous crime like he did, this is a person that is liable to creating violence anywhere they go,” Glendale police media relations manager Jose Santiago said.

“When you have situations like this, all our officers get involve, try and get this person off the street as quickly as they can, and because the last thing they want is to see another family victimized,” he added.

A victim’s advocacy center is working with Cruz Rubio’s family and law enforcement officers who experienced trauma from the “very gruesome, bloody scene,” Santiago said.