The upstate New York man who slit the throat of a 17-year-old Instagram star Bianca Devins after she kissed another man at a concert last year and then posted images of the grisly killing online has pleaded guilty to second-degree murder.

Brandon Clark, 21, of Cicero entered the guilty plea on Monday, Oneida County District Attorney Scott McNamara said.

He will receive the maximum sentence of 25 years to life, according to the prosecutor.

Clark, whose sentencing is scheduled for April, initially pleaded not guilty. His trial was set to begin later this month, the Syracuse Post Standard reported.

In a Utica courtroom on Monday, Clark admitted that he 'sliced' Devins' throat multiple times after he witnessed her kissing another man even though Clark and Devins were platonic friends and not dating.

Brandon Clark (left), 21, of Cicero, New York, will be sentenced in April to between 25 years and life in prison for last year's brutal slaying of Bianca Devins (right), 17

Clark also said he decided to plead guilty so as not to put the victim’s family and his own family through a trial, according to Spectrum News.

He apologized to the judge, saying that Bevins 'didn’t deserve what happened to her.'

'I think I need to realize what I did I can't undo, as much as I want to,' Clark said in court.

'I have to face it.'

Clark continued: 'I apologize to all the people that knew and loved her.

'I apologize to everybody affected by this - everybody who had to see that horrific picture of her.

'I know sorry is not enough and it won’t take back what I did.

'I wish I had more to give.'

Devins, who was known among her 170,000 Instagram followers as an e-girl who posted about emo fashion and video games, was murdered on July 14 after getting into an argument with Clark, who police say slit her throat in a fit of jealousy after she kissed another man at a concert in Queens.

The case drew horror nationwide after Clark, who tried to slice his own throat as police arrived on the scene, posted photos of Devin's body on both Instagram and Discord, a chat app popular among teens.

Clark (seen last year in an Oneida County courtroom) initially pleaded not guilty, but said on Monday that he changed his mind because he didn't want to put his family and that of the victim through a trial

After stabbing himself, Clark is said to have thrown himself on a tarp covering Devins' body and proceeded to take selfies.

Police say the pair had been at a concert in New York City on the night of Saturday, July 13, and that they had driven back to Utica later.

They were in Clark's SUV for several hours.

According to internet chatrooms and comments Bianca made to friends in her final hours, they smoked marijuana together in the car.

Earlier in the night, another young man was with them.

One of Bianca's friends told Rolling Stone on July 16 that Clark had become jealous because he thought she was flirting with the other male.

Messages Bianca sent from the concert indicated that Clark saw her kissing another man, and became jealous.

Utica Police Lieutenant Bryan Coromato said they received a call on the morning of July 14 that led them to the crime scene.

'We got a call from one of the parents that was concerned about some things that were occurring in the relationship at this point,' he said.

Clark posted a photo of her body with the caption 'I'm sorry Bianca' to Instagram, which was criticized for failing to remove it for almost a day.

Devins was known among her 170,000 Instagram followers as an e-girl who posted about emo fashion and video games

She was murdered on July 14 after getting into an argument with Clark, who police say slit her throat in a fit of jealousy after she kissed another man at a concert in Queens

Pallbearers carried Bianca Devins' coffin into the Church of Our Lady of Lourdes in Utica, New York on July 19, 2019

He had also scrawled 'May you never forget me' on the road next to them.

He also allegedly posted a photo on Discord, with the caption 'Sorry f**kers, you're gonna have to find someone else to orbit.'

Orbit refers to the internet slang term 'beta orbiters,' supposedly low-value men who cling to the social media accounts of e-girls in vain hope of reciprocated interest.

After photos of her body emerged online, numerous people called 911 to report it. Police were already trying to find the pair when he called himself.

Police arrived at the scene on the morning of July 14 to find Clark lying on the ground beside a black SUV.

When the officer approached, he began to stab himself in the neck with a knife.

The officer requested emergency medical care as Clark then laid himself across a green tarp that was on the ground, said to have been covering Devins' body, and proceeded to take selfies.

He was subsequently taken to a hospital for emergency surgery, with his injuries described as 'severe' but not life-threatening.