Daniel Pelka was murdered by his stepfather and mother in Coventry
The man convicted of murdering a four-year-old boy who was subjected to "incomprehensible brutality" has been found dead in jail.
Mariusz Krezolek, 36, was discovered in his cell by guards at about 08:30 GMT on 27 January at Full Sutton prison.
He was given a life sentence in 2013 after being convicted of murdering step-son Daniel Pelka in Coventry.
Daniel's mother, Magdalena Luczak, who was also found guilty of his murder, was found hanged in her cell last July.
A Prison Service spokesman said Krezolek was found "unresponsive" in his cell, and despite efforts to revive him he was pronounced dead shortly afterwards.
"As with all deaths in custody, there will be an investigation by the independent Prisons and Probation Ombudsman," they said.
Daniel was starved and beaten for months before he died from a head injury in March 2012 at his Coventry home.
During Krezolek and Luczak's trial at Birmingham Crown Court, jurors heard the boy weighed just over a stone and a half at the time of his death.
He was denied food, poisoned with salt, locked in a small room, forced to perform punishment exercises and subjected to water torture.
The boy had been treated at hospital for a broken arm, and turned up at school with bruises and facial injuries.
A teaching assistant had said he looked like "a bag of bones", and he had been seen scavenging for food.
Mariusz Krezolek (left) and Magdalena Luczak both died in prison after their convictions
The medical evidence, Judge Mrs Michael Cox said, showed that Daniel's emaciation was regarded by experts as "unprecedented" in Britain.
The trial also heard that Luczak, despite knowing of Daniel's hunger, gave specific instructions to his teachers that he was not to eat any more food than his small packed lunch because of an eating disorder.
Judge Cox said Daniel's mother and step-father had acted with "incomprehensible brutality" towards him, causing the boy "severe physical and mental suffering".
Krezolek was sentenced to a minimum of 30 years in jail.
In December 2014, both he and Luczak failed in a bid to reduce their sentences, which they had claimed were "excessive".
Three judges at the Court of Appeal also dismissed Krezolek's bid to overturn his murder conviction.
A serious case review found chances to help Daniel had been missed, and "no professional tried sufficiently hard enough" to talk to him about his situation.
Dr Mohammad Pathan, a GP, was given a warning on 1 July last year for not acting adequately over concerns raised about Daniel.