THE parents of a 16-year-old girl who died in her sleep have been told they will never know for certain what killed her.

Camilla Irvine, known as Milla, from Newton-le- Willows, near Bedale, North Yorkshire, died on September 25, last year, after spending the night at a party with friends.

The inquest into the Richmond School student’s death heard how she fell asleep on the sofa at a friend’s house in Scorton, near Catterick, but, the next morning, she could not be woken.

She was pronounced dead at the Friarage Hospital, in Northallerton.

A post-mortem examination showed that the likely cause of death was an arrhythmic heart beat – a genetic condition with no symptoms, sometimes referred to as sudden adult death syndrome.

No traces of drink or drugs were found, but an unidentified substance was discovered in her urine, which pathologists were unable to definitively rule out as a cause of death.

Forensic toxicologist Dr Simon Elliott tested the substance against more than 6,000 drugs, pharmaceuticals and non-toxic compounds, but could not find a match.

He said: “It could be this was something that naturally occurred in her body, or it could be a new legal high we haven’t come across, but that is very unlikely.

“The fact it was in her urine and not her blood suggests it had no effect on her death but, because we cannot identify what the substance is, we can’t say for certain.”

Pathologist Dr Jennifer Hamilton told parents David and Wendy Irvine that Camilla would have died almost instantly and without pain.

Jacob Atwood, whose house Camilla had stayed at on the night she died, told the Northallerton inquest: “I would swear with my hand on my heart that she did not take anything at that party.

“She was fine, she was happy and she helped to clear up after the end of the party.”

Recording an open verdict, coroner Michael Oakley said the lack of certainty about the unidentified substance meant the cause of death would never be completely clear.