A Brooklyn man allegedly confessed to stabbing his grandmother, admitting the crime to his own mom shortly after the victim was found, authorities said.

“I killed grandma,” Jackson King allegedly said after 85-year-old Julia Boomer was found battered and with multiple stab wounds, according to a criminal complaint.

An unkempt-looking King, 22, appeared in court Saturday to face a murder charge in Boomer’s Jan. 13 death.

Jackson King, 22, was arraigned on murder and weapons charges in his grandmother’s killing. Paul Martinka

Julia Boomer, 85, was found by her daughter with stab wounds throughout her body, officials said. Kyle Mazza/NurPhoto/Shutterstock

King, cuffed behind his back and with his hair uncombed, was wearing black sweatpants, white socks and black slip-on shoes for the appearance before Judge Elizabeth Warin, during which he pleaded not guilty.

The suspect spoke to his lawyer but otherwise said nothing as he was arraigned in front of Judge Elizabeth Warin on charges of murder and criminal possession of a weapon in the killing of Julia Boomer.

Brooklyn Defense Services Lawyer Matt Coretto asked for medical and psychiatric attention for his client, who has been hospitalized since the heinous crime.

Prosecutor Taylor Lupi asked Jackson be sent to jail and the judge agreed, sending King to Rikers Island without bail.

The woman’s grandson told his mom he killed his grandmother, according to a court document released Saturday. Kyle Mazza/UNF NEWS/Shutterstock

Jackson King, 22, lived with Boomer in a Throop Avnue building in Brooklyn. Paul Martinka

Boomer was stabbed multiple times just before 10 p.m. on Jan. 13 in the home she shared with Jackson on Throop Ave. in Bedford-Stuyvesant. 

The victim’s daughter made the grim discovery, cops said. 

Start your day with all you need to know

Morning Report delivers the latest news, videos, photos and more.

Thanks for signing up!

Boomer was rushed to Kings County Hospital in critical condition but couldn’t be saved.

The motive for the killing, which cops called a domestic dispute, wasn’t clear.

King has three prior arrests on his record for grand larceny and criminal contempt, police sources said.

The murder was the first in the NYPD’s 79 Precinct so far this year, police data show.