As the Commonwealth Day service begins at Westminster Abbey, members and friends of the Royal Family have come together to celebrate the King's first as Monarch.
Among many familiar faces, including the Prince and Princess of Wales leading the procession, former Spice Girl Geri Horner has been spotted entering the grounds.
Dressed in a long-sleeved cream jacket and brown cross-body bag, Geri arrived at the royal church full of smiles.
The Ginger Spice is an ambassador of the Royal Commonwealth Society and has launched the Commonwealth Essay Competition for the last few years.
This year's theme is Forging a Sustainable and Peaceful Common Future - and comes at a time when Charles has experienced great turbulence in his relationship with his youngest son, Prince Harry.
Charles is now head of the Commonwealth, following in the late Queen's footsteps after she successfully lobbied for him to take on the role.
A Commonwealth flag for peace will be carried in the procession of Commonwealth members' flags to mark 2023 as Commonwealth Year of Peace.
The service will include musical performances from saxophonist Yolanda Brown, West End stars Roshani Abbey and Nuwan Hugh Perera, and the all-female Amalgamation Choir, from Cyprus.
Guests of honour among the 2,000-strong congregation will include the Commonwealth secretary-general, the prime minister of Samoa, high commissioners, senior politicians and dignitaries from across the UK and the Commonwealth.
Also attending will be athletes from the home nations who competed at the Commonwealth Games in Birmingham last summer, as well as faith leaders, and more than 750 schoolchildren and young people from throughout the UK.
The service will be broadcast live on BBC One.
Since 1977, the Commonwealth Day service has often fallen on the second Monday in March and has its roots in the British Empire.
Originally called Victoria Day, it was changed to Empire Day after Queen Victoria's death. It was introduced to foster a sense of collective identity across what is now a group of countries encompassing over two billion people.
The name of the event was changed to Commonwealth Day in 1958 and it is known as that in the present day.
The Commonwealth website says: "Commonwealth Day is an annual celebration observed by people all over the Commonwealth in Africa, Asia, the Caribbean and Americas, the Pacific and Europe."
The celebration is focused on the shared values of the different countries and includes a range of activities and cultural events.
The event is a symbolic show of unity with Lady Scotland calling for nations of the Commonwealth to "stand together" in the face of widespread global uncertainty.
She said: "In an uncertain world, with multilateralism under strain, the Commonwealth shines as a beacon of hope and promise, inspiring confidence in the benefits of international cooperation and collective action.
"We celebrate the diversity that enriches us, and the similarities that enable us to work together. Our points of unity make the Commonwealth unique in our world. Drawing from the deep wells of our unique history, they enable us to face the challenges of the 21st Century with clarity, unity and purpose."
