The mother of a young boy who died after the outside of their home was engulfed by floodwater which she believes was contaminated with toxic fumes has said she wants to ensure he "dies in truth".
Nicole Lawler described seven-year-old Zane Gbangbola as a gift, as the inquest into his death more than two years ago began.
The schoolboy was killed after serious flooding in Surrey in early 2014. His mother found him not breathing at their home in Thameside, Chertsey, Surrey in the early hours of the morning of February 8, and he died in hospital.
An initial post-mortem examination into Zane's death proved inconclusive. Further tests, which disclosed that his death was as a result of carbon monoxide intoxication, are disputed by his parents.
Ms Lawler and her partner Kye Gbangbola, who was paralysed and is now a paraplegic as a result of the same incident in which his son died, have campaigned for the truth about Zane's death, saying the floodwater was contaminated with toxic hydrogen cyanide fumes from a nearby lake built on a former landfill site.
Zane's parents and grandfather held hands and Ms Lawler was seen to wipe tears from her eyes as proceedings got under way at Woking Coroner's Court in Surrey.
Giving evidence, she said: "Zane was a gift," adding that he was "generous" and "kind".
She added: "He walked in truth. We are here today to make sure he dies in truth."
Ms Lawler said she and her partner "cherished" every moment with their son, adding that they were "so very proud" of him.
Outside court, people gathered with placards calling for "the truth about Zane" and a number of friends wearing a red flower to symbolise their support for the family sat in the courtroom to listen to the evidence.
On the first day of the inquest, which is expected to last until mid to late July, Senior Surrey coroner Richard Travers said: "It is likely that the fact that Zane died as a result of toxicity will not be in contention.
"The question may well be which toxic substance was responsible."
Mr Travers said the inquest will look at whether it is likely Zane died as a result of carbon monoxide poisoning or hydrogen cyanide poisoning.
Addressing the court about the point of an inquest, he said: "I should emphasise that it is not part of this court's function to apportion blame, and by that I mean liability."