Katrina Shangreaux, 30, has been jailed for 40 years for beating her two-year-old son to death after he wet the bed in July 2016

A South Dakota mother who beat her son to death after he wet the bed and gave her 'side eye' has been sentenced to 40 years behind bars.

Katrina Shangreaux pleaded guilty to second degree murder as part of a plea deal in March, after initially pleading not guilty to first degree murder, and was handed down her sentence on Tuesday, The Rapid City Journal reported.

The 30-year-old admitted to beating her son Kylen, two, with a studded belt, throwing him to the ground and hitting him in the stomach and head in a rage when she came home on July 28, 2016, and found the little boy had wet the bed.

She told the court in her confession she had been drinking heavily and was on pain medications before the attack.

In her written statement she said she became even angrier after the boy 'gave her a sideways look' and referred to her as 'Angie' - his paternal aunt Angie Shangreaux, who had custody of him until a tribal court gave him back to Shangreaux weeks before his death.

Assistant U.S. Attorney Sarah Collins told the court during sentencing Shangreaux's brutal beating had left the two-year-old boy with bleeding on his brain, cigarette burns on his head and horrifically mutilated genitals.

Kylen (pictured) had only been back with his mother for a few weeks - after living with his paternal aunt for more than a year - when he was murdered. Chief Judge Jeffrey L Viken told the court the toddler's killing was 'horrific, depraved, torturous [and] humiliating'

Kyren's autopsy revealed he had bleeding on his brain, cigarette burns on his head and horrifically mutilated genitals

While the sentencing guidelines for Shangreaux suggested 27 to 33 years, Chief Judge Jeffrey L Viken increased the sentence due to the 'unusually heinous' crime.

He described Kylen's death as 'horrific, depraved, torturous [and] humiliating', noting the toddler could never have defended himself.

After his death, Shangreaux and her mother, Sonya Dubray, cleaned blood and feces off Kylen, and cleaned up the scene.

When she finally called 911, she told the dispatcher her son had choked on apple juice.

The mother-of-five told Judge Viken it was 'one day that went wrong', and that she feels regret every second of every day.

A Facebook page created by Kylen's aunt Angie to promote the case and fight for a life sentence for Shangreaux reacted to the sentencing, simply posting: 'My poor baby boy'.

Earlier, she wrote: 'I should have never stopped fighting for you. I love you the most Ky Sky Pie. No one can ever take away our love.

'All I know is that this didn't have to happen. It could have been prevented... if someone had listened and done their job.'

Dubray has pleaded not guilty to being an accessory and hindering the investigation. She will face trial in November.

Kylen's father is serving time in federal prison for abuse and neglect of a son with a different woman.

Shangreaux, a mother-of-five, told Judge Viken it was 'one day that went wrong', and that she feels regret every second of every day