Prince Louis' star jumper for fourth birthday portrait has very sustainable backstory

The jumper worn by Prince Louis to mark his fourth birthday has been revealed as having a very sustainable backstory.

In a series of portraits to celebrate his special day, the youngest child of Prince William and Kate Middleton can be seen posing on a Norfolk beach while wearing a grey cashmere knit with multicoloured stars.

The brand behind the cosy sweater, Olivier London, has revealed that the item is from its 2017 collection, a year before the royal birthday boy was born, suggesting that it is a sibling hand-me-down.

Sharing an image of the prince – who was also sporting a checked shirt and green shorts – to Instagram, they wrote: "Happy Birthday Louis.

"Thrilled to see our Star Jumper still going strong, a lovely testament to the long lasting nature of our cashmere. Have a lovely day Louis."

The knit is likely to have previously been worn by Prince George, with his younger brother appearing to have been dressed in a number of his outgrown items over the years.

These include a polo shirt from Rachel Riley and Hampton Canvas slip-on trainers for the Cambridge's 2021 Christmas card.

It is in line with his mother's commitment to sustainable dressing, with the Duchess of Cambridge frequently re-wearing items of clothing.

Read more: The weird rule Prince George followed that Prince Louis hasn't had to

This includes on Easter Sunday, when the royal mother-of-three wowed in a baby blue Emilia Wickstead dress.

The frock had previously made an appearance on an official visit to Luxembourg that she made with the Duke of Cambrige in 2017.

These latest images of the young prince were taken by his mother during the Easter holidays.

In some of the shots, the barefooted young royal can be seen smiling while holding a cricket ball.

Watch: Everything you need to know about Kate and William’s children