Sir John Key on conversations with the Queen and why she sent Prince William to NZ

Former Prime Minister Sir John Key has spoken of his memories of time spent with the Queen, saying he believed she would have been happy that it was at Balmoral that she died because of her love of the place.

Key and his family stayed at Balmoral Castle with the Queen in 2013 for a weekend Key says was "one of my life's great memories".

"It's obviously an incredibly sad day, but the fact that her final time on Earth was at Balmoral will be something she would be very happy about. Because it genuinely was a place that she loved. She loved the rural community, the horses and the beauty of that property.

"And she loved that it was the one place that she got a bit of me-time."

Key said he had often spoken to the Queen when he was Prime Minister, and had received a Christmas card from her every year since then.

The Queen's long life meant she had a different perspective on issues in their conversations together.

"She would say that Prime Ministers were always faced with difficult decisions to make, and real challenges and there often was not a right answer, but to do the thing that you believed was the correct thing to do, was not always the easy thing to do.

"She had huge amounts of grace and warmth, but equally so much history and wisdom that you could ask questions and get answers that came from a perspective and vantage point that probably no other person had seen.

"At Balmoral we spent a lot of time talking about other people who had been there, from Winston Churchill to Ronald Reagan and it was just fascinating to be with someone who had been so deeply ingrained in history."

Queen Elizabeth II and Sir John Key at Balmoral Castle in 2013. Photo / Claire Trevett

He said the Queen was always aware of the importance of preparing for succession.

"She wasn't afraid to address those issues and think about them. Many of the actions you've seen her take over the last decade have been very deliberate."

Key said one example was the Queen choosing New Zealand as the country for Prince William's first official international visit in 2010. Key invited the Queen to open the new Supreme Court buildings in Wellington, but she told him she would like Prince William to do it instead.

"I asked her to come down to New Zealand and she said to me that she probably physically could come but she wanted to send Prince William, because it would be the first time he represented her as the Queen.

"And she said it will be great for William, but it will be great for New Zealand because you'll get enormous amounts of coverage and media attention.

"I think in her heart, she knew that New Zealand was a safe place and a great first point for William to step out, who will himself be a future king. And I think that's just all part of her long-term thought process and the way she went about preparing for a passing of the baton."

In 2013, Key was also asked to help the Queen get support from other leaders to ensure King Charles III would succeed her as the head of the Commonwealth after her death – something that was not covered by its rules at the time.

"I think it was a sign of the confidence she had in New Zealand and the understanding she had of me, that I had a great respect for the monarchy and it would be something I wanted to help out on. They were very appreciative."

He said the Queen was realistic about the possibility of countries moving away from the monarchy to become republics, believing it was a decision for them to make.

However, it was very important to her that the Commonwealth remained stable after her death.

"She was always going to reign for her lifetime, and she is a monarch like no other. She believed that when you took that oath, it was an oath for life.

"But she also knew nothing was forever, and if you want these institutions to remain and be solid then there has to be a clear path forward. "

The Duke and Duchess of Cambridge unveil a portrait of the Queen at Government House with John Key (left) and Sir Jerry Mateparae. Photo / Mark Mitchell

Key is a monarchist, and said the "genuineness" of his conversations with the Queen had reinforced his stand, as had the visits by Princes William and Harry in the wake of disasters such as the Pike River mine disaster, the Christchurch earthquakes and the mosque shootings.

He said the Queen had a belief in service and duty, as well as family.

"All the times I dealt with her, and obviously there were many, I always found her to be genuinely interested in and to have a real affection for New Zealand which transcended far beyond a briefing note or what an official might have told her.

"She loved the country, she'd been there many times. She understood its history and heritage, and it deeply mattered to her how New Zealand was going."