The grandmother of a slain Harlem teenager ripped the girl’s teen boyfriend accused of stabbing her to death, insisting to The Post on Tuesday that he was never good enough for her “beautiful” granddaughter.

Saniyah Lawrence, 16, was killed Sunday night when her baby-faced 18-year-old boyfriend, Zyaire Crumbley, allegedly knifed her in the neck inside an apartment on Adam Clayton Powell Jr Boulevard and then fled, police said.

Hours after Crumbley turned himself in, Lawrence’s paternal grandma, Eileen Lawrence, said she’d always had a hunch about the boyfriend.

“I met him just a couple of months ago and that was it. I made it a point not to even bother meeting him again,” the grieving grandmother told The Post.

“I didn’t think he was good enough for her.”

Speaking after a Tuesday night memorial service for the murdered teen in Harlem, Eileen Lawrence described her eldest granddaughter as a “beautiful person.”

“Everyone loved her. Wherever she went she was like a sunshine,” she said.

“She became a magnet. People just went to her. People who didn’t know her became her friends and loved being around her. That’s the kind of person she was.”

The grandmother added that Lawrence’s grief-stricken father, Justin, was “destroyed” over the teen’s slaying.

“That’s his firstborn so he’s really destroyed knowing this is carelessness — there was no need for her to die the way she did and it’s broken my son up,” she said.

“My son is literally broken.”

Crumbley, who has six prior robbery arrests to his name, has since been charged with his girlfriend’s murder.

He is accused of stabbing Lawrence at about 5.40 p.m. Sunday after the pair got into an argument.

In the moments after the fatal attack, Crumbley was captured on surveillance video fleeing the apartment building and going on the run.

Lawrence was rushed to Harlem Hospital where she was pronounced dead.

Cops subsequently released a youthful-looking mugshot of Crumbley in a bid to track him down before he surrendered to cops Monday afternoon.

While neighbors told The Post the couple had a history of fighting, police sources said it didn’t appear that Crumbley had a history of domestic violence with the teen victim.

Still, domestic violence advocates were among those to address mourners at Lawrence’s vigil Tuesday night.

“Unfortunately we are in front of you today because we had a senseless crime. We had a child that was murdered,” said Stephanie McGraw, founder and CEO of the Harlem-based WARM domestic violence non-profit.

“We can’t eradicate domestic violence by ourselves. It’s going to take a collective village of all of us saying enough is enough,” she continued.

“If you see something we want you to say something because what you might say might save a life.”

Roughly 100 people attended the vigil where white balloons were released by mourners in honor of the 16-year-old.

Lawrence’s funeral will be held Dec. 20 at Harlem’s Unity Church.