The announcement of the Duchess of Cambridge's pregnancy is another step in the monarchy's continual process of renewal, Monarchy New Zealand chair Dr Sean Palmer says.
"It's certainly very nice to hear. I think everyone expected it was going to happen sooner or later," he said.
"There's obviously quite a bit of interest in the monarchy, and future generations of it, as it is in the process of renewing and reinvesting itself, as it does all the time. This is just the next step in that," Palmer said.
"What's particularly interesting about this royal pregnancy is that with the changes to the succession rules, we know that whatever gender this baby is, it will inherit the throne, that this baby will one day be the king or queen of New Zealand."
Asked whether he was being optimistic to think the monarchy would remain New Zealand's head of state for that long, he said he would call it "realistic".
He saw no indication New Zealand was likely to cut its ties with the monarchy on the death of the Queen.
"Particularly in the past three or four years, we have seen a surge in interest and popularity of the monarchy. Every time a member of the royal family is down here their popularity increases. For those who would like to see the monarchy's connection to New Zealand enhanced, that's good news," Palmer said.
"This is New Zealand's royal family, and in as much as we know how monarchies work, we know who the next head of state of New Zealand will be and we know the one after that." That was barring anything unfortunate happening.
Referring to the writings of Canadian historian Jacques Monet, Palmer said it showed something about the faith New Zealanders had in human beings that they would say: "whatever gender, whatever strengths or weaknesses ... that's going to be our head of state".
"In many ways, it's a very democratic concept," Palmer said.
"It says we're all pretty much the same, we all have strengths and weaknesses, and as long as this child grows up with a sense of responsibility to the countries it's going to serve, including New Zealand, then that's all we really expect of someone who is to serve as head of state."
Prime Minister John Key said he was "delighted" to hear the news the pair were expecting a baby.
"This is fabulous news for Prince William and Catherine, and I know the Queen and Prince Phillip will be extremely pleased.
"It is an important day in any young couple's life when a baby is expected and I know that Catherine and William will be as nervous and excited as anyone," he said.
Governor-General Sir Jerry Mateparae noted the announcement of the Duchess of Cambridge's pregnancy was an especially wonderful gift for the Queen in her diamond jubilee year.
"It was with much joy and happiness that we learnt this morning that Their Royal Highnesses, The Duke and Duchess of Cambridge, are expecting a baby," the governor-general said.
"News of the pregnancy is a wonderful gift to the child's parents, and both of their families, and especially Her Majesty The Queen, who celebrates her diamond jubilee this year.
"On behalf of my wife Janine and all New Zealanders, I send our best wishes to the Prince and Duchess at this happy time. I will be writing to Their Royal Highnesses to offer my personal congratulations."