A few hours earlier, he had announced his status was changing from Prime Minister to outgoing Prime Minister.
His usual iron grip on his emotions threatened to cave while he was delivering the resignation speech, his voice cracking.
He says he had written the speech himself - he had to because he had not told any of his staff of his decision until that day. But it still came as a something of a shock to read it out loud.
``I hadn't read it out loud and you're reading it out and all of a sudden it hits you in terms of the enormity of it.''
His announcement is a bit like a ballistic missile for National, but Mr Key goes to great lengths to try to insist National can still win another term without him.
Mr Key has always thrived on people and admits popularity was a factor in his decision.
He insists he was not chickening out because he was afraid he would not win.
``It wasn't a fear of losing. I'm not fearful of losing. And I've made lots of tough decisions and not all of them have been popular, so it wasn't that.''
Mr Key has a competitive streak and the prospect of a rare fourth term must have been tempting.
``In many respects, I would love to go into the election next year and I feel very confident that we would do well.
``I feel confident we will do well, whoever the next PM is. But the question is: did I want to do another two years beyond that?
``You can't do this job without 100% commitment.
Australia's line-up of former and current prime ministers had sent him messages, including Julia Gillard, Tony Abbott and Malcolm Turnbull.
He is also pleased by a ``really lovely phone call'' from Labour leader Andrew Little.
Asked if Mr Little had thanked him for going, he says no.
His children, Max and Stephie, were probably just as pleased as Mr Little to hear he was leaving.
Stephie was back in New Zealand from France for a visit.
``I don't think Stephie was surprised. They were both fantastic. They were both really mature about it.
``I think they wanted to make sure I felt I was making the right decision.
``They've had a degree of pressure and intrusion your average kid doesn't get. They are not silly.
``They understand on the one hand while that's difficult for them, on the other hand the job has afforded them, as well as us as the whole family, remarkable opportunities.
``I hope they are proud of what I have done.''
Max does not plan to follow in Mr Key's political steps.
``He has no intention of retiring from social media, I think,'' Mr Key jokes.
``He was never off it, that was the problem sometimes. But he'll be carrying on,'' he laughs.
``I think Max will have a much higher profile than his dad in months to come.''
The man who has handed out knighthoods like Santa doling out parade lollies is more coy when asked if he would take one himself.
``I've kidded around about it for years but it's not something I've sat there and ... they'll decide if they're going to do something or not.
``In the end, I'm a former prime minister, like a lot of other former prime ministers, the advice will be to do something. That doesn't mean they will.
``I'm happy. I don't need a gong to feel as if I've made a difference as PM.''
He is told his preferred replacement as prime minister, Bill English, has just described him as balder, fatter and ``not the athlete he thinks he is''.
Mr Key giggles. ``Did he? He's right about putting on weight.''
He says what he will most miss are the people who arrange his days - his staff, his colleagues.
He does have one treat waiting.
After eight years of having his assets in a blind trust, once he leaves Parliament he will be able to peek inside it.
As for his post-politics plans, Mr Key laughs when a consultancy with outgoing US President Barack Obama is suggested.
``I wish.''
After the interview proper is over, Mr Key stands there with a smile back on his face as if he cannot believe his luck.
He says while he did not feel the sense of a burden lifting, he did know how lucky he had been to do the job he had and have such a long, golden run at it.
``I've had a dream run,'' he says as if he can not quite believe his luck. ``No-one gets to do what I do.''
One thing is certain. There will be a lot more golf. - The New Zealand Herald
- by Claire Trevett
