Hospital ended with 'heart-breaking' scenes last night when viewers found out a newborn baby never recovered from his emergency heart surgery.
Casey-Jack, who featured in the BBC Two documentary, needed heart surgery soon after he was born because he had a hole in his heart and a damaged artery.
Despite surgeons operating on his heart, which they said was no bigger than a strawberry, he couldn't recover and died last year when he was just two months old.
Viewers tweeted about their upset after learning about the infant's death, which was revealed at the end of the hour-long programme.
They called the episode 'heart-breaking' and 'terribly sad', commending his parents for sharing their tragic story.
Casey-Jack needed heart surgery soon after he was born to repair a hole in his heart and an underdeveloped major artery, but he never recovered from the drastic operation
Last night's episode, the fourth in the six-part series, followed the children's heart surgery unit at Alder Hey Children's Hospital in Liverpool.
Casey-Jack, one of the three children whose stories it revealed, was born with a hypoplastic aortic arch.
This meant he had an underdeveloped aorta – the main artery out of the heart – and a hole in a vital part of the organ.
Doctors discovered the heart defect when his mother – Charlotte – had her 20 week scan.
On the programme, while she and her partner Mark, Casey-Jack's father, are waiting for their son to have surgery, Charlotte said: 'You don't realise how much time, effort and love you have for one person.
'[It's] been rough. Up and down – there are days when you [go] what did I do wrong?'
Mark had 'always wanted a child of his own', Charlotte said on the programme, and 'it hit him hard' when he found out his son was seriously ill.
In the end credits of the programme it was revealed that, despite the surgery being successful, Casey-Jack did not recover and died of heart failure two months after he was born.
Twitter user Steve Shilling described the ending as a 'punch in the stomach'.
Julie Smith said: 'What a beautiful little boy ... R.I.P. Casey-Jack. Condolences to his family.'
Lauren Fordham added: 'Poor Casey-Jack's family, if only every kid got the happy ending they deserve.'
Casey-Jack's mother, Charlotte, revealed she had days where she thought 'what did I do wrong?' when she discovered her baby son had a congenital heart defect
Casey-Jack's father, Mark, had 'always wanted a child of