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 general zest for life that has seen him repeatedly steal the show at royal events, the youngest child of the Prince and Princess of Wales 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.

The snap was posted on the Prince and Princess of Wales’s social media accounts thanking royal fans for all the kind wishes they had sent to the young prince 

And just like 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 has like so many younger siblings always been the star of the show.

Prince Louis has been compared to the cartoon character Boss Baby

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.

The young prince’s cheeky antics went viral as royal fans were left in hysterics at his funny behaviour

Louis got stuck in with a pot of emulsion paint (something I never would have let my five-year-old 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.

A  wonderful one – the picture chosen to mark Prince Louis’ first birthday

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.

Louis was having colourful fun in the shot released for his second birthday

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

Yesterday’s new photograph of the scene-stealing birthday boy was taken by his mother ‘in the last few days in Windsor’, where the family live in cosy Adelaide Cottage. It shows Louis in shorts and George’s checked shirt, his feet bare, smiling into the camera without a care in the world.

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

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.

Aged three, the prince in training was pictured on his balance bike

The picture is understood to have been unedited, deliberately, following the furore that resulted over the princess’s Photoshopped Mother’s Day picture, which saw it withdrawn by international picture agencies. She later apologised for the confusion.

For his fourth birthday, he enjoyed the beach boy lifestyle

Prince Louis with his mother Kate and siblings George and Charlotte in the controversial doctored Mother’s Day photo which was later withdrawn by picture agencies