The Prime Minister made an embarrassing admission when the MPs Register of Pecuniary Interests came out today.
It showed a short term-deposit with a law firm that specialises in foreign trusts.
In his entry, Mr Key lists the Antipodes Trust Group Limited as a debtor.
The company specialises in foreign trusts using New Zealand as their "jurisdiction of choice".
The Prime Minister Office says it's come about because his long-term lawyer, Ken Whitney, changed firms to Antipodes, and took a deposit used to cover fees across with him.
The declaration may be embarrassing to Mr Key who has been questioned by journalists about New Zealand's foreign trust system following the release of the Panama Papers.
The Government has appointed former PricewaterhouseCoopers chair John Shewan to conduct an independent review of the rules around disclosure for foreign trusts based in New Zealand.