One of the defining style icons of our time, the Duchess of Cambridge rarely puts a foot wrong when it comes to fashion.

It’s coming up to a decade since she officially joined the royal family and the mum-of-three has evolved her signature style, making bolder choices as the years have gone by.

In the early days of her marriage to William, the Duke of Cambridge, Kate was rarely seen in trousers (unless it was skinny jeans for a sporting activity), but now she embraces tailoring and the latest trends in a cool, confident manner. Her red carpet gowns are more show-stopping than ever.

Could the same be said of other members of the royal family when they hit the big 4-0?

As Kate celebrates her milestone birthday (January 9), we look back at how her personal style compares to other royals at the same age…

The Queen

The Queen turned 40 on April 21, 1966. By this time, the monarch had already perfected her signature look for public appearances: a knee-length dress and matching frock coat in a vivid colour (to ensure she stands out from the crowd) with gloves, hat and her trusty Launer handbag.

Kate does embrace bold colours on occasion (she always looks stunning in red), but she varies her outfits a lot more than Her Majesty and chooses more casual ensembles for outdoor events and activities.

Princess Margaret

Princess Margaret, who turned 40 on August 21, 1970, shared a fondness for frock coats, sensible court shoes and hats with her sister, the Queen.

Compared to the Duchess of Cambridge, Princess Margaret’s outfits tended to be more formal, though she loved a glittering gown for high-profile events, as Kate does.

Princess Anne

A dedicated follower of fashion, Princess Anne rocked some incredible Sixties mod minidresses and bold Seventies suits in her younger days, and her bouffant hair ‘do became famous in itself.

By the time she turned 40, in 1990, the Princess Royal had toned down her style considerably, but she stuck with the voluminous hair. Kate’s Christmas Day outfits are often similar to Princess Anne’s, featuring classic wool coats accessorised with leather gloves and boots.

Duchess of York

The Duchess of York was already divorced from Prince Andrew when she turned 40 in 1999. During that period, Fergie was often pictured in boxy, dark-coloured skirts or trouser suits.

By comparison, Kate is a lot more adventurous with her style, embracing bright hues, bold prints and trendy silhouettes.

Countess of Wessex

Sophie, Countess of Wessex, turned 40 in 2005, a time when she favoured feminine tailoring, often in white or pale hues.

The Countess managed to side-step many of the worst fads of the Noughties by keeping her style relatively classic, and that’s also what Kate does. While the 40-year-old nods to current trends, she knows how to avoid anything that will date quickly.