Court documents recently disclosed indicate that the surviving brother of Matthew Hertgen, a suspect in the Princeton preppy murder case, had warned their youngest sibling about their brother’s struggles with “visions” just before the young brother was brutally killed.

Matthew Hertgen, aged 31, allegedly used a knife and a golf club to kill his 26-year-old brother, Joseph Hertgen, in a Princeton apartment towards the end of last month. Shockingly, he then proceeded to remove his brother’s eye and consume it.

Another brother later informed the authorities that he had messaged Joseph, advising him to reach out if he needed assistance in handling their troubled sibling, as detailed in a statement of probable cause obtained by NJ.com.

“Will do,” Joseph responded — about an hour before he was hacked to death, the filing shows.

The surviving brother, who had spent several hours with Hertgen the day of the slaying, later told investigators his sibling had struggled with mental health and had been “extremely distressed, despondent and experiencing terrifying visions” in the lead up to the killing.

“Wanting to help him, [the surviving brother] picked Matthew up at [redacted] at approximately 4:30 p.m. [The surviving brother] and Matthew went to the grocery store and then to [the surviving brother’s] residence … where they remained until approximately 10:00 p.m.,” the probable cause statement said.

The surviving brother then dropped Hertgen back at the apartment where Joseph was.

After sending the eerie warning message to Joseph, the other brother also texted Hertgen to invite him on a hike the following day and urged him to “Hang in there.” 

Less than 45 minutes later, Hertgen then called 911 to report his alleged twisted rampage, which authorities said also involved setting the family’s cat on fire.

The grim details emerged as Hertgen — a former college soccer star — faced Mercer County Superior Court on Thursday on murder and animal cruelty charges.

The accused killer faces 30 years to life in prison if convicted.

Authorities still haven’t revealed a motive for Hertgen’s alleged spiral into homicidal madness.