Winston Peters is appealing a High Court decision after it dismissed allegations last month his privacy was breached by a leak to media of his superannuation repayments in 2017.
The Deputy Prime Minister now claims he knows who the person who leaked the documents is, but he has not identified the person.
Last month's ruling found Mr Peters had not been able to identify the source of the leak.
Mr Peters sued then-National ministers Anne Tolley and deputy leader Paula Bennett, the Ministry of Social Development, its former chief executive Brendan Boyle and State Services Commissioner Peter Hughes.
He alleged the department heads were wrong to brief their respective ministers under the "no surprises" policy.
He dropped cases against other multiple National MPs as they left Parliament.
The High Court also ruled Ms Tolley and Ms Bennett had "a genuine interest in knowing the details of the payment irregularity" and, therefore, Mr Boyle and Mr Hughes had disclosed the information "for a proper purpose".
However, the ruling also said Mr Peters' private information should not have been disclosed to the media.
The Deputy Prime Minister paid his own lawyer but taxpayers footed the $1.2 million bill for the defence according to Crown Law.
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