It's the huge royal event that dates back more than 200 years and celebrates the official birthday of the King or Queen.
The annual Trooping the Colour parade on Saturday will see King Charles mark his first official birthday since becoming King last September.
Hundreds of horses and soldiers are set to carry out complex battlefield drill manoeuvres to military music - and many parts of the day will remain as they have done for years under the late Queen, with some royals travelling in carriages from Buckingham Palace to Horse Guards Parade to watch the service.
However, given we are now in the early days of a new reign, there are inevitably things that will be different when the parade takes place...
Monarch on horseback
One major change to the parade compared to the final years of his late mother's life will see Charles riding a horse in the procession.
It has been announced by Buckingham Palace that the King will join the military parade by riding on horseback for the occasion.
It will be the first time since 1986 a reigning monarch has ridden in the parade - with the late Queen last doing it that year.
Burmese was the late Queen's favourite steed for Trooping and ceremonial occasions for 18 years from 1969 to 1986 until the animal was moved to Windsor for retirement.
She then decided that, rather than train another charger for the ceremony, she would in future be driven in a carriage.
Charles will be joined on horseback by son Prince William, who witnessed The Colonel's Review ahead of Trooping the Colour at the weekend, as well as Princess Anne.
Royal's riding debut
Meanwhile, another royal who is said to be set to join the King riding in the procession is his younger brother Prince Edward.
The new Duke of Edinburgh will join his royal siblings and nephew on horseback for the first time in the parade, according to the Telegraph - and it comes after he was seen out riding with his other brother Prince Andrew last weekend.
Edward is the colonel of the newly formed London Guards, an Army reserve battalion, which will help with lining the streets during the event.
Poignant uniform change
Another subtle yet poignant change set to be seen at Trooping the Colour this year will be on the royals' uniforms.
And William already showed off the change last weekend as he braved sweltering temperatures during final preparations to the event.
William inspected his troops on horseback, wearing a bearskin cap and red dress uniform, for the first time as Colonel of the Welsh Guards.
And the epaulettes (shoulder decoration) of the jacket now feature the cyphers of both the late Queen as well as the new one for his father Charles.
Those who are appointed an aide-de-camp to the monarch are allowed to wear the insignia, with William carrying out the position to his father and grandmother.
Other royals who were an aide-de-camp to the late Queen and have retained the role under Charles will also wear both cyphers on the shoulders.
Kate and Camilla's new roles
However, two members of the Royal Family not expected to be in military uniform for Trooping the Colour are Queen Camilla and the Princess of Wales.
Both women were given huge new military roles last year - and this will be the first King's Birthday Parade in their new jobs.
Kate became the Colonel of the Irish Guards - a position previously held by her husband William.
It came as William took over the position of Colonel of the Welsh Guard, leaving Kate to take his place.
At Trooping the Colour, colonels usually wear full military uniform, with some even taking part in the parade on horseback.
And according to the Daily Mail, Kate is also not expected to wear military uniform for the parade and will instead ride in a carriage, probably with Prince George, Princess Charlotte and Prince Louis.
The same goes for Camilla, who was appointed Colonel of the Grenadier Guards, a role previously held by Prince Andrew but had been vacant since he was stripped of his royal titles.
New music
The regiment trooping its colour at the parade this year is the Welsh Guards - a regiment close to the heart of the King.
He was colonel of the Welsh Guards for more than 50 years while he was Prince of Wales before passing the colonel role to William when he ascended to the throne.
And for the occasion, the Welsh Guards have composed several new pieces of music that will be played during the parade.
One has been written by Major Lauren Petritz-Watts, the first female director of music of the Welsh Guards and the first female Army musician to have her composition played at Trooping the Colour.
Change of anthem
Meanwhile, when it comes to music, viewers watching Trooping the Colour at home on BBC1 are likely to hear one very familiar piece of music many times - the national anthem.
But unlike in previous years when royals and spectators alike would have sung God Save The Queen, this will be the first year in more than 70 where people will sing God Save The King.
