Prince George didn’t just get presents when he celebrated his fifth birthday on July 22. He also scored a new royal responsibility.

The third-in-line to the throne is now considered old enough to follow one of the most intractable of royal protocols.

George must bow to his great-grandmother, Queen Elizabeth II – who he calls “Gan Gan” – whenever they meet or part.

Young royals have to follow the grown-up tradition “certainly by age five”, historian Marlene Eilers Koenig told Hello! magazine.

According to Ms Koenig, the Queen is the only person to whom other royals must bow or curtsy: “A Royal Highness does not curtsy to another Royal Highness.”

But while George is now old enough to dip his head to the monarch, there’s one mark of being grown up that is still beyond him.

Uncle Harry’s wedding aside, he’s banned from wearing long pants until he’s seven or eight.

George in his signature shorts and long socks in Berlin in 2017. Photo: Getty

“It’s a very English thing to dress a young boy in shorts,” etiquette expert William Hanson told Harper’s Bazaar.

“Shorts on young boys is one of those silent class markers that we have in England.

“A pair of trousers on a young boy is considered quite middle class. And no self-respecting aristo or royal would want to be considered suburban.”

George’s dress code and need to bow are just two of the strict rules in the regimented world of the Windsors. There’s no vulgar nail polish, no knee-crossing, nude stockings at all times, and more.

You can put away the baby rattles

The Duchess of Sussex may have grown up in California, where baby showers are rampant, but she won’t be calling in an event planner should she be an expectant mother.

Because “they are very wealthy, a lavish baby shower would be seen as highly inappropriate”, royals expert Victoria Arbiter told The Sun.

“There’s nothing they can’t go out and buy themselves.”

No-go food

Last month, the Duchess of Cornwall told MasterChef  judge Gary Mehigan there’s one food that can’t ever be served to royals.

“I hate to say this, but garlic. Garlic is a no-no.”

So as not to have unpleasant breath when talking to people?  “Exactly,” confirmed Camilla.

Shellfish is also off the menu because of the risk of food poisoning or allergic reactions.

There’s a right way to drink tea

Royals are constantly being trotted out at afternoon teas, and there is a specific way they have to drink a cuppa.

The top of the handle of the cup is pinched between the thumb and index finger, with the middle finger placed to support the bottom of the handle, which is always kept in the three o’clock position. Royal women try to sip from the same spot to avoid lipstick stains on the rim.

The Duchess of Cambridge drinks tea to a tee in Malaysia in 2012. Photo: Getty

Hats have a time limit

During the day, royal women wear hats to formal appearances, but they are forbidden after 6pm, when it’s tiara time.

Each royal has tiaras of her own, plus can grab a loaner from the Crown Jewels for really gussied-up occasions – but only married females are allowed to wear the special headpieces.

The one thing in every royal suitcase

When the Queen’s father King George VI died while she was on holiday in Africa in 1952, she didn’t have mourning clothes, and appropriate garb had to be rushed to her plane when she landed at home.

Since then, all members of the royal family are instructed to pack a black outfit when they’re away, in case there is a sudden death.

Not even Prince Philip can do this

According to Sir William Heseltine, a former private secretary to the Queen, nobody can go to bed before the Queen – and she’s a night owl who, at 92, still rarely turns in before midnight.

One royal who found the long evenings “agony” was Princess Diana, said Sir William in 2015. “Diana was driven to such extremes that she’d excuse herself and go to bed, which was thought to be rather bad form.”

Don’t sign here, sir

Members of the royal family aren’t allowed to sign autographs in case their signatures are forged.

While Prince Charles deflects any requests with: “Sorry, they don’t allow me to do that,” he wavered in 2010 when visiting Cornwall residents after floods.

One resident asked Charles for his autograph, and according to a Daily Mail photograher, he “astounded” his protection squad by asking for some paper and a pen, and cheerfully signed, ‘Charles 2010’.