An unnamed source told The AM Show former ANZ CEO David Hisco was stood down because one of his family members used chauffeur-driven cars and charged it back to the company.
ANZ announced Hisco would leave the company after mischaracterising personal expenses as business expenses on Monday.
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Hisco's spending, which was in the magnitude of tens of thousands of dollars, included the use of wine storage and corporate cars.
ANZ board chairman Sir John Key told The AM Show a case could be made for the wine storage, but the bank was most concerned about the use of the cars.
But he clammed up when host Duncan Garner asked him what the cars were actually used for.
"Do you know?" Garner asked Sir John.
"Yeah absolutely I know why," the former Prime Minister replied.
"Let's be transparent, what did he do with them?" Garner said.
"Look I'm not going to go down to the minutiae of every car trip, I mean it's fair enough," Sir John said.
But Garner revealed a short while later a source had told him Hisco had not been the one using the cars.
"I have this on good authority that it wasn't so much David Hisco's use of the car, even though it was billed through him, it was somebody else in the household, is what I understand."
Garner later said on the show the source told him the person using the car was a member of Hisco's family.
"It's not defendable and Hisco had to go... there will be no court cases over this. Hisco's problem was his judgement he should have said no."
Hisco became CEO of ANZ New Zealand in September 2010 and was reportedly paid $3.76 million a year.
He has been temporarily replaced by Antonia Watson until the bank is able to find somebody to take the role permanently.
He moved to Auckland from Melbourne to take the role.