Why Prince Louis’ sixth birthday picture, taken by Princess Kate, almost didn’t happen

His cheeky public antics over the years have led his legion of fans to christen him “Boss Baby” after the Hollywood cartoon movie about a toddler who rules the roost.

But my, how quickly little Prince Louis is growing up.

While he still has the same warm eyes, infectious smile and zest for life that has seen him repeatedly steal the show at royal events, the youngest child of the Prince and Princess of Wales – who is turning six – is big enough to wear Prince George’s grown-up hand-me-downs.

In this case it is a £39 Pepa & Co checked shirt in a delightful new birthday portrait taken by Kate.

And as in AA Milne’s famous poem, Now We Are six – “I’m as clever as clever/so I think I’ll be six for ever and ever” – he is said to be flying at his new school, Lambrook in Berkshire, and proving to be not just good in class but sporty and fun (cricket is his big love at the moment, apparently).

Born on April 23, 2018, on the Lindo Wing at St Mary’s Hospital, Paddington, weighing a very healthy 8lb 7oz, Louis – like so many younger siblings – has always been the star of the show.

Whether it is dramatically holding his hands over his ears at his great-granny’s Platinum Jubilee celebrations, naughtily thumbing his nose at Mummy or pinching his nose at last year’s Trooping the Colour, it’s impossible not to be entertained by his theatrics.

When his father, Prince William, proudly speaks about his offspring, Louis’ name is often accompanied by an affectionate rolling of the eyes, indicating how much of a live-wire he is in private too.

But when I was covering a visit by the Wales family as they helped renovate a scout hut over the Coronation weekend last year, I was genuinely blown away (both as a mother and as a journalist) at how well Louis behaved.

Indeed, all three of the children had impeccable manners.

Louis got stuck in with a pot of emulsion paint (something I never would have let my five-yea rold do, let alone in front of the world’s media) painting a planter, frowning with concentration in acknowledgement of the importance of his task.

And he couldn’t wait to help out with a shovel, shifting spadefuls of sand into a wheelbarrow before insisting on pushing it by himself around the corner to a group of fellow volunteers who were laying a new path.

What was amazing, in the circumstances, was the freedom that William and Kate gave “Lou-bugs” who, at one point, careered past me with his barrow, determined to keep up his work – without a parent, carer or even police officer in sight.

He was deterred from his task only by the sight of his big brother sitting with their papa at the controls of a digger, whereby he promptly demanded he get a turn too.

And an adorable little video I took of Louis eagerly grabbing fistfuls of marshmallows to toast before pretending to faint when he tried a “s’more” – a nice gooey marshmallow sandwiched with chocolate between two digestive biscuits – even went viral.

Tuesday’s photograph of the scene-stealing birthday boy was taken by his mother “in the past few days in Windsor”, where the family live in cosy Adelaide Cottage.

His dark brown hair has been neatly combed to one side and his tongue slightly peeks through the gap in his bottom teeth.

The picture is understood to have been unedited, deliberately, following the furore that resulted from the princess’s Photoshopped Mother’s Day picture, which was withdrawn by international picture agencies.

Kate later apologised for the confusion.

Normally the couple issue a photograph of each of their children to mark their birthdays in advance for use by media on the day itself.

This year they had initially decided not to issue one at all given their recent appeals for privacy at such an “unprecedented” time for their family.

The princess, 42, is continuing her recovery from major abdominal surgery in January and undergoing preventative chemotherapy for the cancer that doctors subsequently discovered.

However, it is understood that she and William changed their minds about the picture overnight – as they were keen to thank the public, and express their gratitude for all the messages they have received on Louis’ behalf.

And, if his wide smile is anything to go by, Louis is a very happy and grateful birthday boy indeed.