Royal baby will have to fit in with George and Charlotte
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Oh, the joy of three! The Three Musketeers, The Three Degrees, the Holy Trinity, Neapolitan ice cream... the best things always come in threes. As Kate and William are now to discover.
And congratulations to them, and George and Charlotte as they welcome home baby brother.
I too have three in the boy/girl/boy sequence so I may have some insight into the pleasure (and pain) ahead for the royal couple.
A friend once said anyone with more children than hands was suspect. She's probably right.
But if you love the noise and chaos it is very tempting after two to go for "just one more". It's like "one for the road": rarely a good idea, always hard to resist.
And, as parenting goes, the leap from two to three is possibly the easiest of them all. You're way past first-time neuroticism and realise that as long as the baby is loved, fed and has the occasional nappy change he or she will be fine.
The jolt is far less severe than the earthquake of the first arrival or the seismic second child.
As my husband puts it: "If life as you knew it is already wrecked, how much worse can it get?"
Third children realise, before the umbilical cord is cut, it is their role to fit in.
Number One's start in life is 24-hour attention and all items within 100 yards fully sterilised. For Number Three the most stimulation is watching the buggy straps being fastened, belted up to follow the other two around. A quick lick of the dummy does the job of sterilisation and crying has become ambient sound to shattered Mum.
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And yet, for all that, the fascinating thing is how well-balanced Number Threes turn out. (Prince Andrew is an exception to most rules).
They develop brilliant "not making a fuss" life skills in their earliest years. And they tend to be emotionally and physically mature from keeping up with the older kids' rough and tumble.
Yet most Number Threes do a great job of hiding that maturity to play their everlasting role of "the baby". Most never give it up and it drives my older two wild.
(Image: AFP)
And it's important to note, Number Threes are naughty (back to Prince Andrew) but "cheeky naughty" not "nasty naughty". The kind you can raise an eyebrow to, though if it had been Number One, you'd have raised the roof.
Esther Rantzen said a parent is only as happy as their least happy child. So with three come three sets of worries. But I adopt the Meat Loaf approach to concerns over school reports, mood swings and illnesses - "Two out of three ain't bad."
A great thing about being one of three is there's always someone to play with. Even better, there's always someone to fight with.
I asked my own Number Three what he thought life would be like for the new royal.
"It'll be good," he said, looking over his shoulder to check his sister was out of earshot. "He'll get away with LOADS."
And he flashed me that grin which ensures he gets away with loads.
So I imagine little will dent the charmed existence of Kate and William's Number Three.
Unless, of course, they go for Number Four.