Before taking their seats in Westminster Abbey for this year's Commonwealth Day Service, King Charles and Queen Camilla exchanged small talk with the rest of the family.
They were seen chatting to the Prince and Princess of Wales and the new Duke and Duchess of Edinburgh, as well as Princess Anne and her husband.
However many royal watchers were left confused as to why Kate didn't curtsy to her father-in-law.
Royal protocol dictates that Kate, along with other female members of the family including including Sophie, Duchess of Edinburgh, Meghan Markle and Princesses Beatrice and Eugenie, must curtsey to the King and Queen Camilla as they are the most senior members of the family. Male royals are expected to bow their heads.
Kate normally does this and we've seen her perform several impressive curtsys for both the late Queen and more recently King Charles.
But they only have to carry out the act the first time they see them each day, which could explain why Kate didn't do it today. It suggests Kate must have seen her royal in-laws earlier ahead of the official event, which kicked off at 2.45.
It's not known how the royal family spent the morning, but Kate and William travelled into the capital from Windsor so they may have popped in to see them on the way through.
The two royal couples arrived in separate cars, but all had to battle strong winds as they walked into the Abbey - which will be the setting for Charles's Coronation in just a few weeks times.
Kate looked sophisticated in an Erdem navy suit with a matching hat and a broach with the Prince of Wales feathers.
Camilla paid tribute to her late mother-in-law by wearing her sapphire and diamond brooch. She teamed it with a sapphire blue wool crepe dress and coat by Fiona Clare, and matching feather beret by Philip Treacy.
The theme for this year's Commonwealth Day, Charles's first as King, is Forging a Sustainable and Peaceful Common Future.
Breaking from tradition, Charles gave his Commonwealth Day Message in person. His late mother always did it pre-recorded or as a written statement.
Drawing on the theme, he emphasised the values of the family of nations from “peace and justice” to “care for our environment” embodied in the Commonwealth Charter, signed 10 years ago.
He told the congregation: “Whether on climate change and biodiversity loss, youth opportunity and education, global health or economic co-operation, the Commonwealth can play an indispensable role in the most pressing issues of our time.
“Ours is an association not just of shared values, but of common purpose and joint action.
“In this we are blessed with the ingenuity and imagination of a third of the world’s population, including one and a half billion people under the age of 30.
“Our shared humanity contains an immensely precious diversity of thought, culture, tradition and experience. By listening to each other, we will find so many of the solutions that we seek.”
He also paid tribute to his “beloved mother”, describing how Commonwealth Day was a moment of pride for the late Queen Elizabeth who “dedicated her long and remarkable life” in service to the “Commonwealth family”.
