Coming in third: What lies ahead for the Duke and Duchess of Cambridge's youngest child?

The Duke and Duchess of Cambridge introduce their third child to the world this week. Photo / AP Photo / Kirsty Wigglesworth

Like his big brother and sister, he emerged into a world that couldn't wait to meet him.

His mum, the Duchess of Cambridge, wore a brightly-coloured dress and his dad, the Duke of Cambridge, wore blue, just as they had when they introduced their two eldest children to the public.

They answered shouted questions and smiled and waved for the sea of cameras outside the $15,000-a-night Lindo Wing.

So far, so same.

But will it always be so for the new prince?

He's the third born and the youngest, and there's a fair chance he'll stay that way — the duke said previously he'd be happy with two children; the duchess is one of three.

Prince George will be moulded to be King. His new younger brother will have a different path. Photo / Supplied

Older brother Prince George will be King and older sister Princess Charlotte will likely have every fashion or hairstyle choice analysed to the nth.

So what lies ahead for the as-yet-unnamed prince?

University of Auckland child development expert, Dr Annette Henderson, said he'll have to find ways to develop his own special skills, so he can find his own identity.

"George is going to be moulded into the future King ... Charlotte doesn't have as many of those kind of restrictions, so she'll develop her own set of skills.

"And the third born ... it's kind of like trying to find how you can develop your own identity that's different from the two paths set out in front of you."

The prince would benefit from older siblings encouraging him to talk and move earlier, so he can keep up, and relaxed parents giving him more leeway — typical experiences of youngest siblings, Henderson said.

The Duke and Duchess of Cambridge introduce their third child to the world this week. Photo / AP Photo / Kirsty Wigglesworth

That freedom could be a force for good or ill.

"You could use that freedom to do really good and socially productive things, or you could have too much freedom and go into the social playboy, where you might be too permissive.

"That could happen with any child, but I think sometimes as parents get more relaxed with younger siblings it might be a little bit easier to go that way."

Flinders University South Australia associate professor Giselle Bastin, a House of Windsor expert, said the prince would have a similar childhood to his siblings.

"I think they'll be presented to us as a threesome ... [Princess] Diana placed enormous emphasis on always treating [Prince] Harry as similar to William, being mindful of the fact [Prince] Charles was always singled out as the heir when he was growing up ... I think they'll try to present these three as equals who are siblings before they're in a royal hierarchy."

Prince George is the heir, second-born Princess Charlotte - following a law change - is the spare. Photo / Supplied

But being free of the burdon of proximity to the throne, the fifth-in-line prince will have fewer royal duties, leaving him more able to pursue a chosen career.

He might not have to join the armed services, a Windsor tradition, but should he do so he will be able to go to war like his Uncle Harry did in Afghanistan. As heir, the duke was barred from active service in war zones.

"He might be like Prince Edward — he joined the Royal Marines for about 10 minutes but then decided he wanted to work in theatre and film and he did. I think this one will be able to exercise similar free range of choices."

Youngest royal children could go off the rails, but courtiers were good at "reining" errant Windsors in, Bastin said.

"It's a big business and there's a lot at stake. Windsor Inc., it's like a giant corporation. They're there by the permission of the people, so they have to look like they're offering value for money or they won't be there."

No matter his choices, the prince will always be in the public eye.

How much so, as the decades pass and other royal babies are presented to the world on the steps of the Lindo Wing, would be up to him.

"He might disappear from view when there are so many other royal stories to tell ... unless [he does something] extraordinary or extraordinarily awful."

KIWI THIRD BORNS SHARE THEIR ADVICE FOR THE NEW PRINCE

Angel Renall, Married at First Sight star

Married at First sight star Angel Renall, left, as a child with her older brother and sister, Jesse and Pandora. Photo / Supplied

From my experience when you're the youngest of three the rules are ready to be broken because your parents can't be bothered enforcing them.

If your siblings have excelled then chances are the pressure is off you. If they haven't then it's your parents last chance so you better hope the first two are really good eggs.

I have a feeling the prince will not be forgotten in the world very easy.

Perhaps pursing the unexpected is always a great idea for a Royal. Don't let the pressure stop you from doing anything.

John Key, former Prime Minister

A young John Key with one of his two olders sisters, Sue. Photo / Supplied

My main advice is to avoid selfies and photos taken by his brother and sister in weird or whacky outfits.

In my experience these have a nasty habit of emerging at 21st and on random Facebook posts.

Lloyd Burr, Newshub political reporter and incoming Europe correspondent

Newshub political reporter and incoming Europe correspondent Lloyd Burr, left, aged one, with his siblings Allen, 2, and Katie, 4, in 1988. Photo / Supplied

One day you'll look back at your baby book, and realise there's hardly anything in it.

Your brother and sister's baby books will be full of exciting observations, hair lockets, cards, and comments. Yours will be empty because mum and dad were so busy.

Get used to hand-me-downs. Your clothes won't be new, your bike will be well-used, and the books you read will be ripped and dirty.

Use your voice. The only way you'll be heard is if you use your voice. The squeaky wheel gets the grease etc. This will infuriate your siblings.

You will constantly be compared to your siblings. Smile and nod, because you'll soon carve out your own niche.

Use it to your advantage. Guilt trip your parents "because you're the forgotten son". You can also get away with more trouble too.

Paula Bennett, National Party deputy leader

I grew up with two older brothers, I was the third child and the only girl.

My brothers would say that I was spoilt and got away with more than they did, but I'm not so sure about that.

My brothers never wanted to hang out with me, they generally regarded me as a nuisance and they picked on me relentlessly.

I blame them for the fact that I was demanding, difficult and generally over the top in seeking attention.

I hope the new prince goes down the same path, cause it was hell to parent, but would be really fun to watch.

Michael Van de Elzen, celebrity chef

It's fantastic being third born!

I always had someone to play with when I was growing up and we had a ready-made team for any inter-family sporting competitions over the summer holidays.