Len Brown's office last night confirmed that the Auckland Mayor has not complied with the council code of conduct rules over a trip to Hong Kong.
Responding to an urgent request under official information laws by the Herald, Mr Brown's chief of staff, Phil Wilson, owned up after chief executive Doug McKay allowed the issue to simmer for two days.
Mr Wilson said he understood Mr Brown did not file an annual return of interests by July 31 under the code of conduct because it was under review at the time.
"As a consequence, elected members - and myself on Len's behalf - did not file returns understanding they would be requested to do so at a later date," Mr Wilson said.
The code of conduct matter is the latest in a string of issues about the trip, which has been shrouded in mystery and controversy.
Mr Brown went to Hong Kong on official business in January without telling councillors. The trip only came to light when Mr Brown's two-year affair with Bevan Chuang hit the headlines last month.
The mayor has refused to answer questions about the six-day trip, but his office said he travelled alone as one of three international guests of a Hong Kong Government-funded "special visitors programme".
Ms Chuang told the Herald that she had remained in New Zealand.
Two Auckland businessmen, Tim Ashton and Nick Love, said after they got off the same flight as Mr Brown, they saw the mayor and an Asian woman ahead talking together.
A source said the woman was an official who met Mr Brown when he got off the plane.
Mr Wilson has told the Taxpayers' Union, which has sought details of the trip under official information laws, that statements about the mayor travelling with someone were being "reviewed through legal channels".