An 81-year-old woman has been sentenced to life in prison for fatally shooting her romantic rival in Wisconsin nearly 40 years ago — and she won’t be eligible for parole until she’s more than a century old.

Mary Jo Bailey, 81, was arrested in Arizona last November and charged with first-degree murder for killing Yvonne Menke, 45, outside her St. Croix Falls apartment in December 1985, according to News 18 in Eau Claire.

Prosecutors said the two women had been dating the same man at the same time — and the twisted love triangle turned deadly when Bailey ambushed Menke as she went to warm her car up before work.

In May, a jury found the wheelchair-bound killer guilty of murder.

And a Polk County judge sentenced her to life in prison Tuesday after reading aloud the heinous details of her crime, which included shooting Menke twice in the head after she fell to the ground.

“I think it needs to be said how brutal and how horrific this crime was — and cold-blooded,“ Judge Scott Nordstrand said, according to the Independent.

The judge said state law gave him very little discretion on the sentencing, which will put Bailey behind bars for 20 years at the very least.

By the time she’s eligible for parole, she will be just over 100 years old.

On the day of the killing, Menke told her daughter she was going out to start the car, News 18 said. But then her daughter heard a “whip-like noise” that sounded like gunshots — and prompted her to look out the apartment window.

That’s when she saw someone clad in a gray dress coat, scarf and stocking cap running away from the scene.

Meanwhile, her mom died at the bottom of a set of stairs that led from the apartment to the street.

An autopsy showed she was shot three times with a .22 caliber gun, the station said. She died of blood loss, and the death was ruled a homicide.

Investigators found snowy boot prints that matched Bailey’s — as well as a note in Menke’s purse that had details of Bailey’s truck, the station said.

The man with whom they were involved — the now-deceased Jack Owen — admitted to police that he had been dating both women for several years.

But his relationship with Bailey had already ended, and he had not seen her in several weeks.

At the time, Bailey told the cops that she did own a .22 caliber pistol, but claimed her boyfriend had sold it.

She also had a .22 caliber rifle, but said she didn’t know how to use it.

Menke’s family had also gotten suspicious phone calls around that time, with the caller asking when the family matriarch went to work.

“I feel the caller was the person who murdered my mom, and I told her everything she wanted to know to make it happen,” her daughter, Julie Connors, said during the trial in May.

No new evidence emerged during the new investigation, according to KARE 11.

But investigators built a stronger case that relied on old interviews, a motive, the boot-print and other factors, the station said.

Authorities later collared Bailey at her Maricopa County home.

Three of Menke’s kids spoke during the sentencing hearing.

“On Dec. 12, 1985, you not only took mom’s life, but you took ours as well,” Connors said. “You sentenced me to a life of fear and guilt. A fear of goodbyes and losing someone loved.”

Bailey — who still claims she’s innocence — did not speak during the sentencing, the station said.

Her attorneys said they plan to appeal.