The Minister for Health Simon Harris was made aware of an overspend at the new National Children's Hospital in August last year, according to an internal memo.
The memo, uploaded here by RTE, shows that Mr Harris was given details of a construction budget overspend of around €191m.
It also states that an additional €200m was sought by the construction firm BAM which won the State contract to build the hospital.
This would bring the potential cost overrun to €391m.
However, Mr Harris reiterated his position that he did not know the final overspend figure until November.
It was also revealed today that both the secretary general and assistant secretary general of the Department of Health were told of a €391m overrun at a meeting about the children's hospital last September.
The release of the memos come after new documents showed that senior Department of Health officials knew that a €400m overspend was coming back in September.
The Finance Minister Paschal Donohoe said today there was no reason to ask about the cost of the National Children's Hospital ahead of the Budget.
He claimed he only discussed general overruns in Health ahead of October's Budget and there was no talk around the spiralling cost of the children's hospital.
Fianna Fáil’s Spokesperson for Health Stephen Donnelly said tonight's revelations were "very, very serious".
"It is hard to see any serious attempt made to curtail the escalating costs. It would seem that instead of tackling them, the Minister withheld this information from both the Taoiseach and the Minister for Finance, despite being in regular contact in the lead up to, and throughout, Budget talks," he said.
“Fianna Fáil were not informed of any details related to this cost overrun during budget discussions or indeed during the review talks which took place regarding the Confidence and Supply arrangement.
“The drip-feeding of important documents that we have seen up to this point is not good enough," he said.