A Harlem man’s threats to “destroy” his wife if she tried to divorce him played out in grisly detail when he decapitated her, slit their daughter’s throat and hanged himself, police and family members said.

Police called to check on the family Wednesday night found all three dead in their blood-drenched, second-floor apartment on a tony block of West 121st Street.

Husband Yonathan Tedla, 46, a computer tech at Columbia University, first killed his wife, Jennifer Schlecht, 42, a career humanitarian who advocated for women refugees.

Using a silver hunting knife with a four- to five-inch blade, Tedla slashed her throat with such force that she was beheaded, police sources told The Post.

Her body was found on the bathroom floor, with her severed head resting on her lap.

Tedla then slit the throat of their 5-year-old daughter, Abayesh, leaving her nearly decapitated in her bedroom, sources said.

Finally, Tedla used a length of rope to hang himself from the girl’s bedroom door, the sources said.

The couple, who reportedly met at Columbia University’s Mailman School of Public Health when Schlecht was studying social work, were a fixture on the tree-lined block.

The 6-foot-tall Tedla often strolled the sidewalk with the girl sitting happily on his shoulders, neighbors said.

“I would always see him take his daughter to school, they always seemed happy,” said neighbor Patricia Brodin, 40.

But the couple had been going through a bitter divorce after seven years of marriage, family and police said.

Tedla had threatened in recent days that if she tried to divorce him, she would lose and he would win, the tragic woman’s’ father, Kenneth, 75, told The Post.

“He’d destroy her, or take them all out if she pursued a divorce,” he said of Tedla’s threats.

On Tuesday, Schlecht went to get a restraining order to keep Tedla away from her and the girl — but courts were closed for Election Day, the dad said. She planned to try again Wednesday but apparently never made it to court, the father said.

Schlecht’s concerned brother called the NYPD that night, asking for a wellness check — and at 9:20 p.m., arriving cops discovered the bodies, officials said.

“This is horrible,” said neighbor Michele Carvalho, 47. “Like the devil was right here last night and nobody heard nothing.”

There were no past domestic incident reports involving the couple, police said. But Schlecht had obtained a temporary restraining order against Tedla in 2016, her ­father said.

Schlecht was a career international humanitarian who devoted her life to helping women and girls driven from their homes by war and ­disaster.

“She was a leader in the field of family planning and humanitarian response, and chose to work from New York so she could have more time with her darling daughter,” according to a statement issued Thursday by Schlecht’s colleagues at Family Planning 2020 — a group that advocates for reproductive health care for women and girls in Africa and Southeast Asia.

“She delighted in telling us about her daughter’s first day of kindergarten and the clothes she picked out all by herself,” read the statement, which was signed by the group’s executive director, Beth Schlachter.

Additional reporting by Olivia Bensimon, Tina Moore and Laura Italiano