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The outfits worn by the Royal Family have fascinated many - from the Queen's rainbow coats to the Duchess of Cambridge's tiaras.

But fans of the royals will have noticed that they have never seen Prince George in a Spiderman T-shirt or Catherine in a tracksuit.

There are etiquette rules governing what members of the Royal Family wear to public engagements - from gloves, to military uniforms, and skirts instead of jeans.

Here we reveal the dress code the royals aim to follow.

When the Queen will wear a hat

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The Queen has become known for her bright and bold hats which she is often pictured wearing while performing official engagements.

Dress code etiquette states that women wear hats for formal events, says Diana Mather, a senior tutor for The English Manner etiquette consultancy.

"Up until the 1950s ladies were very seldom seen without a hat as it was not considered 'the thing' for ladies to show their hair in public.

"But all that has changed and hats are now reserved for more formal occasions."

One of the Queen's hats became a hot topic on social media when she officially opened Parliament last month.

Using the hashtag #QueensSpeech, many users compared her floral blue hat to the EU flag.

Why Prince George always wears shorts

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Unlike many three-year-olds, Prince George has yet to be seen wearing a T-shirt of his favourite TV character or a even pair of trousers.

Experts say this is because it is royal tradition for young princes and princesses to be formally dressed when they are in public.

Instead, Prince George is much more likely to wear a pair of smart shorts and a shirt.

Etiquette expert Grant Harrold, known as The Royal Butler, says the tradition dates back to the times of breeching in the 16th Century.

He said: "This saw young boys wearing gowns or dresses until the age of eight, if not before.

"Thankfully in late 19th Century and early 20th Century this developed into shorts. This tradition is carried on by the Royal Family to this very day."

Prince George: The traditional clothes royal children are dressed in

The Queen and her gloves

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No self-respecting lady would be seen without gloves, says Mr Harrold, who tweets etiquette tips via @TheRoyalButler.

Gloves were traditionally considered a fashion item but also had a practical purpose too - helping stop germs being spread from person to person.

With the Queen shaking hands with hundreds of people every year, they serve as a fashion statement but also protect her from bacteria.

"Let's not forget she doesn't always wear gloves when meeting people, therefore it depends on what she is wearing, where she is and what she is doing," Mr Harrold adds.

Keeping it casual

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In private, who knows whether the Duke and Duchess of Cambridge lounge around in matching onesies.

But there is still a dress code to adhere to when dressing casually and being seen in public.

For ladies, a smart day dress or trousers teamed with a jacket or cardigan is considered acceptable while for gentlemen it is a blazer with a collared shirt and chinos.

Prince William and Catherine tend to follow these traditional rules but sometimes let their modern edge slip on a dress-down day - by wearing jeans.

"Many places will not allow jeans as they are still seen as very casual wear, so it is better to play safe for both sexes," says Ms Mather.

"But if the duchess is outside walking the dogs for example, then jeans are fine."

Trooping the Colour

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Fans of the Royal Family will not have failed to notice that the Queen's wardrobe encompasses all the colours of the rainbow.

She is reported to have once said: "If I wore beige, nobody would know who I am."

Mr Harrold credits the monarch's personal assistant Angela Kelly for the bold colours she often wears while on duty.

It is said that the Queen wears bright colours to ensure members of the public stand the chance of seeing her through the crowds.

"She loves colour and knows it will stand out - good for her I say," says Ms Mather.

Military style

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Prince William and Prince Harry have both served in the armed forces and have been pictured wearing military uniforms.

The royals often wear their uniforms when they represent their regiments at occasions which are military affairs, such as the Trooping the Colour or services to honour British troops.

Prince William served in the RAF but also holds the title of Colonel of the Irish Guards - which has a striking red uniform.

He chose to represent the regiment by wearing its colours for his 2011 wedding to Catherine.

The crown jewels

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The Duchess of Cambridge is unlikely to have been seen in public wearing a tiara before her wedding.

This is because they are reserved for married women or members of the Royal Family.

Tiaras are traditionally worn at formal events, especially when the code is evening dress, says Ms Mather.

"The old rule is that hats are never worn indoors after 6pm, because that is when the ladies changed into evening dress, and tiaras and the family jewels would come out.

"Flashy diamonds and tiaras are not worn during the day, and only married ladies wear tiaras."

Mr Harrold adds: "For married ladies it was a sign of status and would show you were taken and not looking for a husband.

"For the gentleman it was a clear sign not to make advances toward the lady in question."