Two-month-old Cody Shields-Holman suffered ‘fatal head injuries’ at a house in Bamford, Derbyshire, and was taken to Sheffield Children’s Hospital on June 27 - he died two days later.
Anton Shields, 39, of Hardwick Crescent in Athersley South, was arrested at the scene and subsequently charged with murder, a charge he denied.
Just a day before his trial was set to begin, he pleaded guilty to a lesser charge of manslaughter.
This plea was accepted and the murder charge was dropped after detailed discussions between Cody’s family, prosecutors and the police.
Shields was sentenced to nine years in jail at Derby Crown Court on Tuesday.
Following the sentencing, Cody’s mother - who was not named - issued a statement which said: “I have lost my baby forever but I think of him all the time.
“Cody would have been approaching one-and-a-half years old now and I often think of what he would be able to do, if what happened had never happened.
“Our family's lives were ripped apart that day.
“I had no concerns about Anton being left with Cody, as I had done it before - but that simple decision to leave them for 15 minutes ended in devastation.
“Cody was eight weeks old when he died and had changed so much in those eight weeks - he was my bundle of joy, his brothers and sisters adored him too.
“I put on a brave face to be strong for my children - I have to.
“I’m their mum and they need me but it has been very difficult to explain to them what happened, especially to my youngest.
“All I could say to him was that his baby brother had gone up to be a star in the sky, and watches down on him every night.”
The detective inspector who led the police investigation into the baby’s death, Steve Bruce, admits that only Shields knows what happened in those 15 minutes he was left alone, but hopes the sentence can bring a small sense of justice to the family.
He said: “My thoughts on this extremely difficult day go to Cody’s mother and family, whose lives were shattered by the actions of Anton Shields in those 15 minutes.
“Only Shields knows what truly happened in those moments, but what we do know is that Cody was assaulted to such an extent that he suffered fatal head injuries.
“What this case highlights is just how devastating such an act can be - it shows how fragile a baby’s body is, and why they need to be nurtured with the utmost care.
“Cody came from a loving home - he was doted on by his mother, adored by his siblings and loved by all of his family.
“It was only when he was left in the care of Shields, as he had been before, that this happened.
“No sentence can undo what happened that day but I hope it brings some small sense of justice for the family, and for the close-knit community of Bamford.”