A seemingly fit and healthy nine-year-old boy died just a week after coming down with the common cold.
Tristan Ang, from Milipitas, California, died after developing adenovirus, a particularly aggressive form of the viral infection.
The martial arts-obsessed youngster had recently competed in a national Taekwondo competition in June - a sport in which he had gained a black belt.
His devastated family have now issued a warning to other parents to remain vigilant about the illness, after they failed to spot subtle signs of the dangerous condition.
They said it "could happen to any kid".
His symptoms were so subtle that his parents - both of whom are nurses - did not realise how ill he was and prescribed Paracetamol to manage his fever.
Tristan was later taken to hospital by his concerned mum and dad when his condition failed to improve.
Doctors said he was likely dehydrated and was sent home to recover and told to drink plenty of water.
But his health took a dramatic turn for the worse as he became confused and disorientated and was rushed to the nearest intensive care unit.
Medics discovered that he had signs of brain swelling but tested negative for meningitis .
Adenovirus typically causes a sore throat , congestion, coughing and fever and shows up with other signs of infection.
Despite showing few other symptoms of adenovirus, Tristan's brain continued to swell and his organs began to fail.
"After the fourth go, that’s when the doctor told Belle and I that he’s dying", dad Mark told NBC Bay Area.
"As a nurse, I know. But as a dad, I don’t want to believe it."
Tristan's heart stopped a total of four times before he was pronounced dead on June 28.
Adenovirus is a highly contagious infection and has recently taken the lives of 11 children in New Jersey alone.
His parents say he will be sorely missed by them and his two younger siblings.
“He would just hug you out of nowhere, kiss you, tell you he loved you,” his mum Ang told the San Francisco Chronicle.
“He was such a good-hearted kid. I know he would have helped a ton of people.
“I hope other people can draw something from what’s happened to us, even if it’s just, love your kids. Hold them close, because you can lose them so fast.”
