The family - and the first Maori member of royalty, Davina's husband Gary - are notoriously publicity shy. Until today in the Herald on Sunday, they hadn't revealed the baby's name - even to Lewis' family in West Auckland.
One women's magazine writer speculated they were trying to lie as low as possible. "Precariously-linked royals are not keen to fall out of favour."
Proposed changes to the Royal succession rules, removing the discrimination in favour of male heirs, will make little Tane Mahuta Lewis' connection to the throne tenuous.
Every time another little girl or boy is added to the inner branches of the Mountbatten-Windsor family tree, he will fall further down the list.
And, ironically, the little New Zealander has the country of his forefathers to thank. It is New Zealand that is chairing an international working group, co-ordinating the 16 realms that have the British monarch as head of state, to ensure the changes go through smoothly.
And it is the New Zealand Parliament that has revealed, for the first time, plans to speed the changes so they are introduced to the UK Parliament by the end of this year. That would ensure that, should Prince William and his wife Catherine have a baby daughter, that little girl can take her place with confidence in the line of succession. She would be third in line after her grandfather and her father, and that position would never be jeopardised by the birth of a baby brother or if she chose to marry a Catholic. (Though, if she herself converted to Roman Catholicism, she would be blacklisted).
The fact the changes are coming is no secret; the plans to introduce them by the end of the year will be a shock to traditionalist Royal-lovers.
The rules of succession have been in place for centuries: no Roman Catholics can rule the United Kingdom, no one married to a Roman Catholic can rule, and the Crown is always passed to the eldest male, wherever possible.
Last year at the Commonwealth Heads of Government Meeting in Perth, heads of state agreed to gender-neutral succession, based on the order of birth.
Instead of all descendants of King George II having to obtain royal permission to marry, only the first six in line to the throne need seek the Queen's permission. (Harry's not off the hook yet, should he be tempted by another naked romp with the girls in Las Vegas - he'll still have to call his grandmother before tying the knot in a drive-thru wedding chapel).
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New Zealand Republican Movement chair Lewis Holden says the failure to tackle the monarch's role as head of the Church of England means we will be put in the ludicrous position of having to pass a law that breaches our own Bill of Rights. That Bill prohibits discrimination on religious grounds, but the new succession laws will still deny Catholics the throne.
Holden seems resigned to such archaic contradictions. When you're dealing with the monarchy, he says, a lot seems ludicrous.
New Zealand is one of the few realms that has the rules of succession written into its laws, so we will need to pass legislation to enact the changes. Other realms simply designate Britain's head of state as their own.
If many do not need to legislate, it'll be a small job for the New Zealand Cabinet Office to get everyone into line - but if it requires new laws in every tiny realm, the process could take much longer.
And it's vital they agree. If someone opts not to change the law, the next Queen could find one of her realms presided over by her brother or uncle - even if he is prone to getting naked.
Auckland University constitutional law expert Bruce Harris says the Queen as the head of state for New Zealand is a different legal entity to the head of state of other realms.
So if, for example, New Zealand agreed to the change and Australia didn't, each side of the Tasman could be ruled by a different member of the Mountbatten-Windsor dynasty. Some are deciding it's all a bit too much bother - Jamaica is to become a republic anyway; the Bahamas are undergoing a constitutional review. One thing won't change: male or female, Anglican or Catholic, monarchy or republic, the young Royals will continue to fill the pages of our women's magazines.
New Idea editor Louise Wright says her readers don't much care whether the next Royal baby is heir to throne or not- the entire Royal Family are simply behind the times. "They're just dragging themselves into the 21st century."
Heir today, a homeopathic doctor in Germany tomorrow
If the monarchy had not been quite so averse to having a woman in charge, history would have been very different.
In 1509, Margaret Tudor would have taken over from Henry VII - meaning her brother, Henry VIII might have lost the opportunity to divorce and behead quite so many wives - and he may not have made the seminal 1533 break from Rome.
Elizabeth Stuart, known as the Winter Queen of Bohemia, would have followed her father, James I, on to the throne in 1629, instead of Charles I. England might have escaped civil war and Charles might have avoided execution.
If the Act of Settlement hadn't been passed in 1701, giving the throne to Electress Sophia of Hanover and her firmly Protestant descendants, we might have Francis II of Bavaria as our King. He's regarded as the rightful heir to the House of Stuart but instead he lives in an apartment in Munich, collecting modern art.
If the changes were made as recently as last century, a second Queen Victoria would have followed her mother on to the throne in 1901. Historians say this might have been a good idea: She was thought to be wiser than her younger brother Edward VII, whose interest in all things French, particularly women, resulted in the Entente Cordiale that destroyed relations with Germany.
And when she died just a couple of months into her reign, her son, Kaiser Wilhelm II would have taken over, putting a German on the throne for the first part of the 20th century. It's likely neither of the world wars would have happened.
Queen Elizabeth II would have spent her life as a minor princess and it would likely have been a woman by the name of Friederike Thyra Marion Wilhelmine Dorothea von der Osten parachuting into the Olympics with James Bond. Instead, last anyone heard of her, she was working as a homeopathic doctor in Germany.
Even this century, lives would have changed. Canadian Autumn Kelly would not have had to convert from Catholicism to Anglicanism to marry the Queen's grandson, Peter Phillips - although the £500,000 ($990,000) Hello magazine reportedly paid for their story may have helped that religious transition.
George Windsor, Earl of St Andrews, wouldn't have had to give up his place in line for the throne because his wife wouldn't convert, and neither would Edward Windsor, Baron Downpatrick, nor Prince Michael of Kent.
The changes to the rule of primogeniture are expected to take effect beginning with William and Harry, the sons of the Prince of Wales. But if they were applied to all of Queen Elizabeth's offspring, then Peter Phillips' mother Anne would soar up the rankings, from 10th to fourth in line to the throne. Peter would be promoted from No11 to 5, and his older daughter would follow him in sixth place, creating the possibility of a monarch with the unlikely name of Queen Savannah.
Back to the New Zealand heirs, though, and it's little Tane Mahuta, the son of Gary Lewis and Lady Davina who would suffer the biggest fall in the Royal line of succession. He'd disappear down the rankings immediately, dropping from No 26 to No 40. Judging from his family's very Kiwi aversion to the spotlight, he might not think that is such a bad thing.
