The Colorado man who pleaded guilty to killing his pregnant wife from Clifton, along with their two daughters, is telling his story from behind bars in a new book.

In the book, Christopher Watts, 34, says if he never met his mistress, Nichol Kessinger, he would not have killed his family. Watts also claims he still loves Kessinger, who he met at work and had been seeing for two months before the murders.

Watts pleaded guilty to killing his wife, Shanann, 34, back in August 2018, along with their daughters Bella, 4, and Celeste, 3.

Watts strangled his wife in their bed at their home in Frederick, Colorado, also causing the death of his unborn son, Nico.

He then drove his daughters to a remote oil field where he worked, and smothered them in their blankets before squeezing their bodies through eight-inch hatches and dropping them into oil tanks.

He told investigators his daughters were not alive when they went into the tanks, and he had intentionally separated their bodies.

He rolled his pregnant wife's body into a shallow grave.

Watts says he murdered his family so he could be with his mistress.

Watts was sentenced to five life sentences last November without the possibility of parole after pleading guilty to avoid the death penalty.

The book, Letters From Christopher, is on pre-order and will be published Oct. 7.