'Our kind and funny teenage son told us he was feeling unwell on the phone — it was the last time we ever spoke to him'

From the outside, David Aitken never appeared to be ill from his diabetes.

Even when he was diagnosed - aged just 12 - his only symptom was thirst. But three weeks short of his 20th birthday, a complication of the condition suddenly claimed his life.

For his parents Zoe and Gary, who were travelling home from a holiday in March last year when they learned of David's death, the news was unfathomable. The day before, David had spoken on the phone about a possible stomach bug but reassured his parents that his blood sugar levels had been "fine all day", Wales Online reports.

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What they did not know was that it had been some time since David's levels were fine. Although thriving at the University of South Wales and loving student life in Cardiff, David had recorded an extremely high blood sugar level in early January. Zoe and Gary say they had not been told.

The couple, from Whitland in Carmarthenshire, do not blame the NHS for their son's death but they believe stretched resources may have led to missed opportunities to save him. Hywel Dda health board has promised a "thorough clinical review" of their concerns. Zoe, 59, told WalesOnline: "David was kind and funny, and he would have been just such a lovely man if he got that far. We feel it's such a waste. It needn't have happened."

Although David was only 20 seconds younger than his twin sister Sian, she always assumed the "big sister" role, said Zoe, who is raising funds for Diabetes UK in David's memory. Sian has always been well-organised, while David was more "whimsical". Gary, 63, recalls an occasion when David remarked solemnly aged five: "I wish I was four again, I liked being little." Another