Kate Middleton apparently can’t wear this when flying

When it comes to royal fashion, there are many rules to follow, and it may surprise you to hear that includes travel too.

For example, Kate Middleton's dresses have their own seat on the plane for this reason, she often has to wear hats when she lands, and royals always travel with this one outfit for this slightly morbid eventuality.

And while it's tempting to think the Duchess of Cambridge might just like to travel in comfies like the rest of us, it seems like there's a protocol for that too.

According to etiquette expert Anne Chertoff, who spoke to Express.co.uk, royals have to dress up as a sign of 'respect' to the people they are visiting.

'When members of the Royal Family are on an official state trip on behalf of Queen Elizabeth II they are working, just as anyone else on a business trip. It’s appropriate for them to dress well to show respect to the people they are meeting with.'

So that's why you'll never see Kate stepping off a plane in jeans and trainers, with no makeup on and her hair in a bun.

That said, we'd like to think that behind closed doors, say on a long haul flight on a private jet, she would change into some sweats and comfie socks. You never know.

Penny Goldstone

Penny Goldstone is the Digital Fashion Editor at Marie Claire, covering everything from catwalk trends to royal fashion and the latest high street and Instagram must-haves.

Penny grew up in France and studied languages and law at the Sorbonne Nouvelle University in Paris before moving to the UK for her MA in multimedia journalism at Bournemouth University. She moved to the UK permanently and has never looked back (though she does go back regularly to stock up on cheese and wine).

Although she's always loved fashion - she used to create scrapbooks of her favourite trends and looks, including Sienna Miller and Kate Moss' boho phase - her first job was at MoneySavingExpert.com, sourcing the best deals for everything from restaurants to designer sales.

However she quit after two years to follow her true passion, fashion journalism, and after many years of internships and freelance stints at magazines including Red, Cosmopolitan, Stylist and Good Housekeeping, landed her dream job as the Digital Fashion Editor at Marie Claire UK.

Her favourite part of the job is discovering new brands and meeting designers, and travelling the world to attend events and fashion shows. Seeing her first Chanel runway IRL at Paris Fashion Week was a true pinch-me moment.