The detail has escaped from a court hearing about the internet tycoon's finances.
It matches up with a trigger date which passed in September meaning he no longer needs government permission to purchase the home.
Crown lawyers told the High Court in Auckland that Dotcom was planning to buy the mansion.
In the hearing, Crown Law Office lawyer Anne Toohey expressed concern over the purchase and Dotcom's new business venture, an encrypted cloud network dubbed Mega. "There is a concern how this new venture is being funded."
The mansion was said by Crown lawyers to be worth $21 million.
Dotcom has recently sent Twitter messages about investors for the new business flying into the mansion.
Lawyers acting for his wife, Mona, have also told the court he is attracting support and interest from new backers simply because he was still "sucking air" almost a year after he was arrested for extradition to the US on criminal copyright charges, which he has always denied.
Lands Minister Maurice Williamson originally approved Dotcom's application to buy the mansion last year. Three months later, the minister changed his mind after then-Justice Minister Simon Power vetoed the approval.
Yesterday, Mr Williamson said "by virtue of his incarceration and his being held" that he would soon be able to buy the mansion without any restrictions.
The trigger date had actually already passed.
Dotcom was granted residency under the investor category and returned to New Zealand in late September last year. By staying in New Zealand for six months out of 12 months he became "ordinarily resident" in late September.
The description means he can buy property as if he were a New Zealander.
- By David Fisher of the NZ Herald
