The woman having an affair with Colorado killer dad Christopher Watts called him “disgusting” as she broke down thinking about him smothering his toddler daughters, an interview revealed.

“Why? Why? Why?” Nichol Kessinger, 30, yelled during an Aug. 16 interview with Colorado Bureau of Information agents, according to audio and video released last week.

“I don’t even understand how you can like bring yourself to do that to somebody who is like that big,” Kessinger says about the deaths of Bella, 4, and Celeste, 3, before breaking down into tears.

“Those little girls … they’re so little,” she said.

The two-hour interview, uploaded by the Denver Post, took place three days after the murders of Watts’ pregnant wife, Shanann Watts, 34, and their two children.

Chris Watts confessed to strangling his wife and pleaded guilty to murdering his entire family in exchange for prosecutors sparing him the death penalty.

“Ugh. He’s so disgusting, I’m so ashamed of him,” Kessinger told investigators.

“I’m gonna wake up every day and know that like this mom and her unborn child and these two little girls are not around anymore and it breaks my heart.”

“You know, they’re gonna say, ‘Oh, you know, you’re the woman that had an affair with this man who took out his whole family,'” she added.

Kessinger, who worked with Watts, had been dating him for less than two months when his family disappeared.

Watts told her he was separated and getting ready to divorce and she only learned the truth about his life after news outlets began reporting on the disappearances, she said.

“He lied about everything,” she told the Denver Post.