Seán Dunne's US bankruptcy trustee has accused him of "acting in utter bad faith" and seeking to thwart a settlement with the property developer's ex-wife, Gayle Killilea, over fraudulent asset transfers.
The trustee is now seeking to have Mr Dunne sanctioned by a court in Connecticut, where he filed for bankruptcy with debts of €700m in 2013.
The move comes after Mr Dunne's lawyers indicated he was seeking a temporary injunction in the New York Supreme Court to stop one of his sons using millions of euro in a Swiss bank account to facilitate Ms Killilea's settlement with the trustee.
Richard Coan now wants to intervene in that case, which has yet to be heard.
In a legal filing, lawyers for the trustee described as "demonstrably false" claims by Mr Dunne (65) that he is seeking the injunction to safeguard funds due to be paid into a trust for four other children, who are all minors.
The case was moved to the United States District Court for the Southern District of New York yesterday following an application from the trustee and Mr Dunne's son John.
The one-time 'Baron of Ballsbridge' is seeking an injunction temporarily restraining John Dunne (32), his son from his first marriage, from accessing funds held by Yesreb Holding Ltd.
If secured, the injunction has the potential to scupper or delay the settlement agreed between the trustee and Ms Killilea (44), who was Mr Dunne's second wife.
Cyprus-registered Yesreb is owned by John Dunne and was loaned €15m by Ms Killilea to buy Dublin mansion Walford from her in 2013.
The property was subsequently sold for €14.25m in 2016 to a trust linked to financier Dermot Desmond.
Mr Dunne's injunction application centres on the proceeds of that sale, said to be "less than €13.5m", which were put in an escrow account in Switzerland.
Last year, a US jury ordered Ms Killilea to pay the trustee €18m for the benefit of her ex-husband's creditors, including €14m relating to Walford, following an action by the trustee over fraudulent asset transfers. A settlement has since been reached, but is awaiting finalisation. It involves the transfer to the trustee of the money held by Yesreb.
But in legal papers, lawyers for Mr Dunne say he wants an injunction to stop his son John dissipating Yesreb's funds, as he claims these are owed to a trust for the benefit of the four young children he had with Ms Killilea. This has been disputed by Ms Killilea's lawyers, who say the four children have "no direct claim whatsoever" to the funds.
They also say the injunction proceedings will be "extremely detrimental" to the long-term interests of the children, which would be better-served by resolving existing lawsuits.
Lawyers for Mr Coan say Mr Dunne's claim is "demonstrably false" and his intentions obvious. "He is not 'protecting' his children. He is interfering with the trustee for his own personal gain," they said.
Their affidavit cited testimony previously given by Mr Dunne in which he said he did not believe his son John held the ownership of Yesreb for the benefit of his four half-siblings.
It also cited testimony given by John Dunne last year in which he stated he and the children were only to benefit if the proceeds of the Walford sale exceeded the €15m loan from Ms Killilea.
The affidavit said it was notable that when John Dunne gave this evidence, lawyers for his father did not cross-examine him on it or elicit any testimony contradicting him.