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• Republic debate: Australian leaders call for head of state
His New Zealand counterpart was not as enthusiastic about change. Mr Key said it was likely Australia would become a republic before New Zealand.
"I don't think there's any chance New Zealand is going to become a republic anytime soon. In fact, I would be amazed if New Zealand becomes a republic in my lifetime. And I'm hoping to live a long and happy life."
He said he would also be surprised if Australia moved that way soon.
Labour leader Andrew Little, a republican, was hopeful of change earlier than Mr Key had forecast and said he would like to be the Prime Minister that led the debate.
However, he did not intend to push it. "Right now I don't see there is any appetite from most New Zealanders to change our constitution."
He agreed it would become an issue of discussion when the Queen's reign ended and believed both countries would become republics.
He said Australia had already had a referendum in 1999 and had a republican Prime Minister in Mr Turnbull. "So it doesn't surprise me that there's a sense of momentum, or at the very least that it's further to the surface politically than it is here."
He said it would not necessarily be a catalyst for New Zealand to move if Australia did. "We have to do it in our own time, at our own pace."
Mr Key is a fan of the monarchy and cites cost savings in favour of the status quo. He believes there is loyalty to the Royal family.
"The bond with the Royal family has been growing stronger and closer in the last 10 to 20 years, particularly with the young royals. I just think there is no appetite to become a republic."
He said it was a separate question to the issue of the flag.