royal family
The Duchess of Cornwall, the Prince of Wales, Queen Elizabeth II, the Duke of Edinburgh, and Duke and Duchess of Cambridge (L-R) arrive for the annual evening reception for members of the Diplomatic Corps at Buckingham Palace in London, Britain December 8, 2016. Picture taken December 8, 2016. Reuters/Dominic Lipinski/Pool

Kate Middleton looked regal in Princess Diana’s tiara and Queen Elizabeth’s diamond necklace at the Spanish State Banquet on Thursday. However, there’s something missing. The Duchess of Cambridge was the only member of the royal family who was not wearing a sash.

The feast, which was held to welcome King Felipe and Queen Letizia of Spain to the UK, saw Kate in a lacy blush Marchesa gown. However, she wasn’t wearing a sash, unlike her husband, Prince William, and other members of the British royal family, who all had some form of sash draped over their upper garment. So why was Kate not wearing one?

The sashes are called “orders” and have various types. As the Harpers Bazaar explains, the most famous of these types is the Order of the Garter, which the Queen bestows on senior members of the royal family and 24 “knights.” The knights used to be from aristocracy only, but they can now be selected for their contribution to public life.

All the Queen’s children are members of the Garter, as well as her grandson William, who was appointed Royal Knight Companion of the Most Notable Order of the Garter in 2008. Contrary to some beliefs, the sash is not exclusive to those born in the royal family. Royal wives are given the Royal Victorian Order or the Royal Family Order of Queen Elizabeth II. Camilla, the Duchess of Cornwall, and Sophie, the Countess of Wessex, both have their own sash. Therefore, Kate, who was born to regular, non-royal parents, can own one someday.

It’s taking Kate a while to receive the honour, though. The Countess of Wessex was appointed in 2004, five years after marrying Prince Edward, the Earl of Wessex. Camilla was appointed in 2007, two years after marrying Prince Charles. Kate married William six years ago in 2011.

Kate’s sash may be delayed in coming because she’s a granddaughter-in-law, rather than a daughter-in-law, and therefore she’s not as closely related to the Queen as Sophie and Camilla are, according to People. It could also be Kate’s comparatively low workload. Apparently, although Kate is taking an increasing number of engagements, she still hasn’t taken on as much as the others.

The mother of two undertook 140 engagements in 2016, while Sophie and Camilla did 179 and 221 respectively. That’s not to say Kate was just being lazy. Her number is smaller in part because she takes care of two toddlers – Prince George and Princess Charlotte – at home.

But again, the bestowing of the honour is ultimately up to Queen Elizabeth. She may give Kate a sash after some time or she may not give it at all. If the Queen descended from throne without giving Kate a sash, it would then be up to Charles to give her one if he deemed it fit.

This is not the first time Kate has gone without a sash in a formal affair. In December, she arrived at the reception for the members of the Diplomatic Corps at Buckingham Palace in a red dress and without a sash, while her husband and in-laws each wore one. (See main picture.)