Attorney General John Larkin has directed the coroner to open a new inquest into the death of a girl at the centre of the hyponatraemia inquiry.
Claire Roberts died at the Royal Hospital for Sick children in Belfast in 1996.
In January, an inquiry into the deaths of five children from hyponatraemia in Northern Ireland’s hospitals found that four of them were avoidable.
Hyponatraemia occurs when there is a shortage of sodium in the blood.
Claire’s parents Alan and Jennifer Roberts have protested for 21 years that the truth about their nine-year-old daughter’s death was concealed and that the findings of her inquest were wrong.
Mr Roberts welcomed the direction for a fresh inquest into his daughter’s death, from Mr Larkin.
“As Claire’s parents we welcome the decisive and definitive action taken by the attorney general,” he told the BBC.
He said that between 2004 and 2006, false and misleading information had been supplied to the coroner.
“As a result (of that), the coronial system was undermined and we, as grieving parents, were failed and misled.”
He added: “It is a matter of great concern that between 2004 and 2006 a concerted effort was made by the Belfast Trust to have Claire’s case excluded from the ongoing public inquiry. “
In January, Mr Justice O’Hara, who chaired the public inquiry into hyponatraemia, concluded that the first inquest into Claire’s death was wrong.
He also said there was a cover-up into her death which was not referred to the coroner immediately in order to “avoid scrutiny”.