The stepfather of murdered schoolboy Daniel Pelka refused to be taken to hospital with a bowel condition while in prison over fears he would be recognised, a report said.
Mariusz Krezolek, 36, and partner Magdelena Luczak, were convicted of one of the country's worst child cruelty cases after four-year-old Daniel was starved and beaten.
Daniel weighed just 1st 9lbs when he died aged four in March 2012 in Coventry.
Krezolek and Luczak were sentenced to at least 30 years in jail for murder and both have since died in custody.
A report into Krezolek's death at HMP Full Sutton, near Pocklington, Yorkshire, in January 2016 reveals he had previous medical complaints but refused hospital treatment.
Nigel Newcomen, Prisons and Probation Ombudsman, wrote: "Mr Krezolek had been treated for a fistula in prison and inflammatory bowel disease but refused to go to hospital for treatment, as he said he was afraid he would be recognised.
"He continued to refuse to be referred to hospital for treatment or to be admitted to the prison's inpatient unit.
"He told healthcare staff that he was afraid he would be recognised if he went to hospital.
"His offence had attracted a high degree of media interest."
Krezolek rang his cell bell and complained of chest pains at around 3am of January 27, with a nurse suggesting he travel to the prison's healthcare centre for an electrocardiogram which he refused.
The report said: "The nurse wanted to take Mr Krezolek to the healthcare centre for an ECG to rule out heart problems but Mr Krezolek refused to go and said he would see the doctor the next morning."
When officers began unlocking cells around five hours later, he was found unresponsive.
Staff began resuscitation attempts and an ambulance was called, but Krezolek was confirmed dead just before 9am, with a post-mortem confirming the cause of death as a heart attack.
The report by the Prisons and Probation Ombudsman also reveals Krezolek twice attempted suicide after his partner hanged herself at HMP Foston Hall, Derbyshire, in July 2015.
It said: "In September he told a consultant psychiatrist that he had tried to hang himself twice in the previous fortnight.
"He was moved to the inpatient unit and prescribed an antidepressant."
An inquest at Hull Coroners' Court concluded Krezolek died of natural causes.
During his final months, Daniel Pelka was denied food, forced to perform punishment exercises, confined in a locked box room, poisoned with salt, and subjected to water torture.
A judge at Birmingham Crown Court said "unimaginable acts of cruelty and brutality" were inflicted on the child.
Luczak's trial heard Daniel was regularly "imprisoned" for prolonged periods of time in a small, unheated room at his home.
The door to the box room had been adapted by Krezolek so Daniel could not escape or even see out of the keyhole.
Passing sentence in 2013, Mrs Justice Cox said: "It is a particularly grave aggravating feature in this case that, before the fatal blows to his head, Daniel was the victim of chronic and systematic starvation."
The medical evidence, the judge said, showed Daniel's emaciation was regarded by experts as "unprecedented" in Britain.
The trial also heard 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.