It's one of the few events that's cemented in the diary of nearly every single member of the Royal Family - and it's taking place today, Saturday June 17.
Trooping the Colour, the sovereign's birthday parade, takes place in London, with this year's event set to be very special.
It will be the first of King Charles' reign and will see nearly all of his royal relatives, including the Prince and Princess of Wales and their children, take part in the celebrations.
As well as the parade, the day will be topped off with a balcony appearance by the royals and a stunning flypast by the RAF. Here's everything we know about Trooping the Colour 2023...
What is Trooping the Colour?
The annual event of Trooping of the Colour has marked the official birthday of the King or Queen for more than 260 years.
The ceremony involves hundreds of horses and soldiers carrying out complex battlefield drill manoeuvres to military music.
More than 1,400 soldiers, 200 horses and 400 musicians come together for the display.
The royals will travel from Buckingham Palace down The Mall to Horse Guards Parade in a procession - either on horseback or in carriages.
At Horse Guards, they then watch the military display before joining the procession back to Buckingham Palace once it is over.
After the parade, the royals then gather on the Palace balcony for a march-past and the fly-past by the RAF, which includes the Red Arrows, and will conclude the day's celebrations.
Last year, Trooping the Colour was the event that kicked off four days of celebrations for the late Queen's Platinum Jubilee.
When will Trooping the Colour take place?
Trooping the Colour will take place today, on Saturday (June 17), with the event starting at 10am sharp.
The event nearly always takes place in June to commemorate the monarch's birthday - even though the King was actually born on November 14.
So why would the King wait so long between the two dates for his celebration? Well, it seems it's down to the most British thing ever, the weather.
Edward VII, who reigned from 1901 to 1910, was also born in November - not the best time of year for a huge outdoor celebration - so held it in the summer instead.
The monarch after Edward VII - George V - helpfully had a birthday in June, but the Queen's father, George VI, whose birthday was in December, reintroduced the tradition of an official birthday, which Elizabeth II, who had an April birthday, continued.
What roles will the royals play at Trooping the Colour?
It has been confirmed that the King will join the first birthday parade of his reign on horseback, marking the first time in more than 30 years that a monarch has ridden at Trooping the Colour.
Charles will take the salute as Colonel in Chief of the seven regiments of the Household Division at the Birthday Parade on Horse Guards Parade on Saturday.
It will be the first time the reigning monarch has ridden at Trooping the Colour since 1986 when Queen Elizabeth II last rode.
Also riding on horseback will be Prince William, Princess Anne and for the first time, Prince Edward.
Charles will also be joined by Queen Camilla and members of the Royal Family, including Kate, Prince George, Princess Charlotte and Prince Louis, to view the 1st Battalion Welsh Guards Troop their Colour at Horse Guards Parade.
Members of the Foot Guards and Household Cavalry will also march past the King as will the King's Troop and the Royal Horse Artillery.
They will travel to Horse Guards Parade in a series of carriages alongside other royals. A 41 gun salute will also be fired from Green Park.
After the parade, the King, accompanied by Camilla and other family members, will return to Buckingham Palace for the RAF fly-past, which will conclude the day’s celebrations.
Which royals will appear on the Buckingham Palace balcony?
It has not been confirmed as yet by Buckingham Palace which royals will appear on the balcony for the RAF flypast.
In years gone by, the late Queen used to invite all members of her extended family onto the balcony at Trooping the Colour.
However, at the last Trooping, the balcony was limited to working royals only, with the same happening at King Charles' Coronation last month.
This meant there was no place for the King's younger disgraced brother Prince Andrew nor his estranged son Prince Harry.
Buckingham Palace officials have refused to say whether Harry and wife Meghan Markle have been invited to Trooping the Colour.
The couple were officially invited to the Coronation last month, where Harry attended the historic event solo before leaving straight after the ceremony in order to get back to California for Archie's fourth birthday.
What time will the RAF flypast by the Red Arrows take place?
The flypast by the RAF is set to take place at 1pm while members of the Royal Family watch from the Buckingham Palace balcony.
The route for the flypast is yet to be officially confirmed, but the Military Air Shows has revealed an air restrictions map which shows the expected official route.
It is likely to follow a similar plan for the Coronation, although that was slimmed down due to poor weather conditions.
Around 70 aircraft are expected to take to the skies, and will take off from 15 different locations around the UK before joining forces across the south-east of England, before flying across London.
The proposed restrictions are in the vicinity of the North Sea, East Anglia, Essex and London, before flying over Buckingham Palace at 1pm.
Can you get tickets to Trooping the Colour?
Tickets to watch Trooping the Colour from the grandstands at Horse Guards Parade are allocated by ballot.
People can apply for up to four tickets, with each costing £30.
However, it is now too late to get tickets for this year's event as those lucky enough to come out of the ballot have already been informed.
How else can I watch Trooping the Colour?
But for those without tickets, there are still ways to watch Trooping the Colour.
For those wanting to see the action in person, spectators can gather near Buckingham Palace and on The Mall to see the royals in the procession and on the balcony.
The event kicks off at 10am and anybody wanting to watch from the sidelines is encouraged to get there by 9am.
Meanwhile, Trooping the Colour will also be broadcast live on Saturday morning on BBC1.
The coverage starts at 10.30am and will be presented by Huw Edwards as well as veteran JJ Chalmers.
