A Tennessee grandpa fatally shot his wife and 6-year-old grandson before turning the gun on himself in an apparent murder-suicide, police said.

Terry Majors, 64, is suspected of gunning down his wife, Leigh Shea-Majors, 61, and his grandson, Ty Dodson, late Saturday in a scene that the boy’s 4-year-old sister witnessed, Metropolitan Nashville police said.

He then took his own life inside the home in Nashville’s Hermitage neighborhood.

That prompted the little girl, Majors’ granddaughter, to run to a neighbor’s house for help, WKRN reported, though her uncle, Chase Dodson, said he believes Ty told his sister to run just prior to the slayings.

The children had been at their grandparents’ home for a routine visit prior to the shootings, Dodson said.

An investigation is ongoing and a motive in the killings has not yet been determined, a police spokeswoman told The Post.

Shocked neighbors, meanwhile, said the Majorses were a helpful and friendly couple, with Terry often mowing lawns for those in need.

“I’m just as dumbfounded as everybody else is to why something like this had happened,” neighbor Chely Wilson told the station. “I know that they loved their grandkids very, very much.”

Tabitha Collins, Ty’s former preschool teacher, said the youngster was a friendly boy who liked science class and aspired to become a police officer.

“He was constantly smiling and wanting to take care of everyone,” Collins told WKRN. “He has a little sister that’s in preschool this year who he walks in and just makes sure that she would get to school and in the classroom OK.”

Collins, who got emotional over the boy’s death, said she simply didn’t want to believe he’s gone.

“It’s just, why?” Collins said. “He’s so young.”

An online fundraiser set up in Ty’s memory had eclipsed $5,700 as of midday Monday.