A churchgoing Brooklyn grandmother was nearly decapitated when her crazed husband killed her with a kitchen knife in front of her 4-year-old grandson Sunday, police and relatives said.

The victim, Hazel Robinson, 51, was attacked about 11:45 a.m. by her husband, Ian Robinson, in the home they shared on E. 102nd St. in Canarsie, relatives and police sources said.

Ian Robinson, 58, went berserk and stabbed her in the neck, partially severing her head, police sources said. The victim’s grandson, who was in the home, watched the horrific attack.

“It was gruesome,” said Lydon Laing, Hazel Robinson’s brother. “He witnessed everything.”

“She wasn’t a bad person. He turned out to be,” said the victim’s brother Arthur Laing, 60.

“God will take care of him.”

Ian Robinson was charged with murder and criminal possession of a weapon late Sunday night. Police said he had no prior arrests and that there had been no previous reports of domestic abuse at the couple’s home.

Charges are pending against Ian, who was taken into custody at the scene.

“She is a very hardworking person, very Christian-like,” Laing said of his sister, still referring to her in the present tense.

Hazel Robinson worked at the Salvation Army in the Bronx, he said.

The couple wed about 12 years ago in their native Guyana.

Before Sunday, there were no signs of trouble in the marriage, relatives said.

Hazel Robinson had an adult son from a previous relationship and a 4-year-old grandson, relatives said.

She was a devoted parishioner at the Christian Cultural Center in East New York, Brooklyn.

“She loved her family,” said the victim’s cousin Claire Hodge, 65.

“She was very concerned about her husband — she took good care of him.