According to newly-updated “protocols” approved by Queen Elizabeth II, Duchess of Cambridge has been placed firmly down the royal pecking order.

A document is said to have been circulated privately in the Royal Household, clarifying Kate’s status.

Despite being the future Queen herself, as a former commoner, the once Kate Middleton must apparently show reverence to the “blood princesses”.

This means Kate is expected to curtsey to those born royal, such as Princesses Beatrice and Eugenie – both in public and in private.

The rule only applies when her husband, Prince William, is not present.

Royal observers suspect Kate will not mind the new rules as she is keen to please everybody, but Prince William may be less happy.

In his absence, Kate must also curtsey to other blue-blooded women in the Royal Household including Princess Anne and Princess Alexandra, the Queen’s cousin.

In the case of the Countess of Wessex, it is she who will have to curtsey to Kate – even though she is a generation older and is married to the Queen’s son, Edward.

According to new protocols, Kate Middleton is expected to curtsey to those born royal, such as Princesses Beatrice and Eugenie, both in public and in private

The Earl of Wessex’s wife was once the second-highest ranking woman in the Royal Family because neither of the Queen’s other sons, Prince Charles and Prince Andrew, were married.

This is effectively Sophie’s second “demotion”, having been pushed down the list in 2005 after Prince Charles married Camilla, and finding she was expected to curtsey to the Duchess of Cornwall.

The complex new rules come in a little-known edict entitled the Order Of Precedence Of The Royal Family To Be Observed At Court, which the Queen has updated to take into account Prince William’s wife.

When Prince William is with her, Kate does not need to bend the knee to either Beatrice or Eugenie.

But she must always curtsey to the Queen and the Duke of Edinburgh, the Prince of Wales and the Duchess of Cornwall, whether Prince William is present or not.

The thorny question of how Kate would fit into the UK’s first family has long been a subject of speculation among royal observers.

The Princess Royal, for example, is said to have refused to ever curtsey to Princess Diana or to Camilla, on the basis they were outsiders whereas she had given her whole adult life to royal service.

In an effort to avoid an epic battle of royal egos, the Queen drew up the first Order of Precedence in 2005, after Prince Charles married Camilla.

Its effect was to change the order along “blood lines” so that Princesses Anne, Beatrice, Eugenie and Alexandra – the granddaughter of George V – were all ahead of Camilla.

The etiquette, though arcane to some, is taken very seriously by the royals, who bow and curtsey to each other in public and behind closed doors.

The Order of Precedence affects other aspects of royal protocol too, such as who arrives first at an event. For example, Camilla was forced to wait in the drizzle outside the Guards Chapel, Windsor, for the arrival of Princess Anne at a memorial service in 2006, because Prince Charles had not accompanied her.

Royal historian Brian Hoey, an expert on court protocol, predicted when Prince William married Kate that: “Kate will take the rank of her husband, which means that when she’s at court, Princesses Beatrice and Eugenie should curtsey to her. But I don’t think there’s a chance they will.”

While Prince William feels warmly towards his cousins, Beatrice and Eugenie, he’s conscious of the fact that they are lesser royals.

“As future King, he will wish to see them behaving correctly towards their future Queen – but their attitude is likely to be: <<Why should I? I was born royal – Kate wasn’t>>.”