The Royal Family Order is an honour granted personally by the monarch to female members of the royal family in the form of a badge, as a gesture of thanks for their service.

When you see the royals wearing various sashes and badges, these are representing different orders of merit and chivalry, however The Royal Family Order doesn't have an accompanying sash.

The ivory badge features a portrait of the monarch, in this case young Queen Elizabeth II, set in diamonds and surmounted by a Tudor Crown, suspended from a chartreuse yellow ribbon. Each monarch has their own colour. They are worn on the left shoulder at white tie events, and if a sash is worn over the left shoulder, the order is pinned to it.

The Queen wears The Royal Family Order of her father, George VI, and her grandfather, George V.

As for who receives the honour and when, it is entirely up to Her Majesty. It is a personal and private gift and the criteria is unknown.

The women currently entitled to wear this order are The Duchess of Cornwall, The Countess of Wessex, and Princess Anne, plus one of The Queen's cousins and two cousins-in-law.

The Duchess of Cambridge is the only senior member of the Royal Family not to have the order. This could be due to a few reasons. For a start, Kate has only been part of the royal family for six years, and while she is taking on an increasing amount of engagements, other senior royals who currently hold the order carry a more full-time position.

Camilla and Diana received their orders relatively quickly, perhaps because they married the direct heir to the throne. Sophie received hers five years after her marriage. Sophie also became a Grand Dame Cross of The Royal Victorian Order, as did Camilla, which comes with a sash — the highest personal honour for service to the monarchy.

Kate's position is not as close to The Queen as Camilla, Diana and Sophie who married into the family as The Queen's daughters-in-law. Kate is The Queen's granddaughter-in-law, and none of Her Majesty's granddaughters hold the order.

Interestingly, Sarah, The Duchess of York never received an order.

At the end of the day, there’s no rhyme or reason to it — it’s all up to The Queen.