Queen Consort Camilla opened the gates of Buckingham Palace this week to welcome a number of European royals for a special event.
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King Charles's wife hosted the likes of Queen Rania of Jordan, Queen Mathilde of Belgium, Crown Princess Mary of Denmark, and the Countess of Wessex for a Violence Against Women and Girls Event.
WATCH: Crown Princess Mary curtseys deeply for Queen Consort Camilla
Guests of honour included Olena Zelenska, the first lady of Ukraine, former Spice Girl Mel B and television presenter Lorraine Kelly, and Carrie Johnson, the wife of former prime minister Boris Johnson.
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The women all came together Palace to raise awareness of violence against women and girls as part of the UN 16 days of Activism against Gender-Based Violence.
Camilla with Sophie Wessex, Queen Mathilde, Queen Rania and Crown Princess Mary
The gathering of royalty offered a fascinating glimpse at protocol within their circles – notably, who was required to curtsy to the Queen Consort and who was not.
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A video from the event shows Camilla greeting Queen Mathilde and Queen Rania inside the palace. In both cases, the ladies embraced each other with a kiss on the cheek.
The Queen Consort greets her counterpart Mathilde inside Buckingham Palace
Crown Princess Mary, meanwhile, followed suit before curtsying deeply to Camilla.
As the same royal rank as the Queen Consort, Mathilde and Rania are not required to curtsy to Camilla, while Mary – as a Crown Princess – is.
Following the death of the Queen, major changes were made in the way that British royals address King Charles and Camilla.
Crown Princess Mary is required to curtsy to the Queen Consort
The Prince and Princess of Wales and Prince Harry and Meghan Markle, for example, would be expected to curtsy or bow when first meeting the couple. If the gesture is not performed it would have meant that they have already greeted the monarch and his wife in private.
According to the British Monarchy website, there are "no obligatory codes of behaviour", but it notes that many people prefer to "observe the traditional forms".
The Prince and Princess of Wales show their respect for the late Queen
As previously mentioned, for ladies, that includes a small curtsy while for the men it is a "neck bow", from the head only. Alternatively, it notes, some may opt to shake his hand.
The gestures don't need to be long or exaggerated – a subtle bow or curtsey is adequate.
Other 'do's' for a royal meeting are; only speak when you are spoken to and do not sit or begin to start eating until the monarch has done so. One should also be early for an appointment with a royal – guests should always arrive first.
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