The teenage son of a 63-year-old English teacher and author was charged with murder Tuesday night for pummeling her to death with his fists, police said.

Karyn Kay died Tuesday just hours after she made a desperate 911 call to tell cops her son was hitting her in their Manhattan apartment, police sources said.

Kay was screaming when she told the 911 operator the 19-year-old Henry Wachtel was having a seizure when he started beating her, a police source said.

Cops rushed to the Hell’s Kitchen building on W. 55th Street at Eighth Avenue just before 9:30 a.m., police said, and found a badly beaten Kay face-up and unconscious on the living room floor.

Neighbors said they were alerted to the horror by shouting.

One said he could hear the son. “He was screaming, ‘I’m sorry mommy! I’m sorry mommy!’ over and over and over,” said one neighbor who lives three doors down from Kay’s 10th-floor flat.

“Then suddenly it all stopped.”

When police arrived, they found Wachtel there - covered in his mother’s blood - when cops arrived, police sources said.

His clothes were being analyzed as he was being questioned at the Midtown North Precinct stationhouse Tuesday evening, the sources added.

Kay was taken with severe trauma -- including a fractured skull and eye socket and broken ribs - to Cornell Hospital where she died at 1:52 p.m., police sources said.

There was no indication Wachtel used a weapon in the deadly attack, police said.

“The police took him in handcuffs. He kept apologizing to his mother the whole time - he kept saying, ‘I didn’t mean it,” neighbor Jonathan Cohen, 49, said the building’s doorman told him.

“He was extremely upset, wailing and crying,” said another neighbor. “When they took Karyn out on a stretcher, she wasn’t moving and her face was covered up with cloth,” he added.

Kay, who works as a teacher at La Guardia High School and is listed as a visiting instructor at Pratt Institute in Brooklyn, lived with her son for more than five years wrote and produced “Call Me”, a feature film that won awards for screenwriting, a Pratt Institute spokesman said.

“This woman had so much faith in each and every one of her students,” said former pupil Jelani Cornick. “She never gave up on us...She took her time out to help me because she cared.”La Guardia High School senior Alessandra Rao said Kay helped assemble the annual “Lively Arts” magazine at the school that celebrates and showcases students’ poems, short stories and artwork.

“She was a beautiful woman inside and out,” Rao said. “Ms. Kay believed in all of us--she found beauty in so many of our pieces, and truly made each one of us feel special.”