Update 4pm: It has been confirmed the cost of the new national children's hospital will be over €1bn - more than one and a half times the last estimate in 2014.
The Cabinet approved the project today, with the foundations to be laid within weeks at the site next to St. James's Hospital in Dublin.
The new facility will open towards the end of 2021.
The rising cost of construction and longer than anticipated planning and procurement processes are partly to blame for the increased cost.
Project Director John Pollock says this will be value for money.
"Back in 2014 we identified those and we said the project would cost €800m, so it was never a €650m project and we were clear to the Department and the HSE," he said.
"Construction inflation has added about €140m to the project, and then our tenders came in about €40m more than we estimated.
Earlier: The Cabinet is today signing off on the construction of the new national children's hospital.
It has been dubbed the most expensive hospital in the world, with a reported price-tag of €1bn.
The facility will be built alongside St. James's hospital in Dublin's south inner city.
On his way into Cabinet, Health Minister Simon Harris refused to be drawn on the actual cost, but insisted he will outline that it is value for money.
“This afternoon there will be a detailed briefing for the media on the costs, outlining exactly the rationale behind the costs.
“But I make absolutely no apology for making a very significant investment in the healthcare of children.
“Children account for about 25% of our population and I think when people see the figures later they will realise that the €650m cost that was envisaged previously related to a point in time. There are a number of significant changes that have been made.”