It's a big day for King Charles today - his first Trooping the Colour since becoming monarch.
The event, also known as the Sovereign's Birthday Parade, is an annual fixture in the calendar.
It sees the royals ride horses or in carriages from Buckingham Palace to Horse Guards Parade to watch an incredible military service before delighting crowds with a palace balcony appearance.
But despite it being held to mark the monarch's birthday - Charles doesn't actually turn a year older until later in the year on November 14.
So why would he hold his birthday parade in June? Well, it seems it's down to the most British thing ever, the weather.
Since 1748, Kings and Queens have marked their big day with the Trooping the Colour parade.
But 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 instead, he moved Trooping of the Colour to May or June because there was less chance of it being cold and drizzly on the big day.
The monarch after Edward VII - George V - helpfully had a birthday in June, but the late Queen's father, George VI, whose birthday was in December, reintroduce the tradition of an official birthday, which Elizabeth II continued.
When Prince William takes the throne in future, two birthdays might not be on the cards though - that's because his actual birthday is in June anyway, making it perfect for a summer celebration.
And the next king, Prince George, is also a summer baby born in July so there is a chance the tradition may disappear for several decades.
At this year's Trooping the Colour, the King, William, Princess Anne and Prince Edward will ride on horseback during the display, while other members of the Royal Family, including Kate and the Queen, will watch from carriages and the Buckingham Palace balcony.
Over 1,400 parading soldiers, 200 horses and 400 musicians take part in the display of military precision, horsemanship and fanfare.
The parade travels from Buckingham Palace down The Mall to Horse Guards Parade and closes with a Royal Air Force fly-past.
This year's fly-past will be extended this year after the display on Coronation day last month had to be scaled down due to bad weather.
The event will feature a mix of aircraft, ranging from the Battle of Britain Memorial Flight dating back to the 1940s and the C-130 Hercules on its final ceremonial flight to multiple Typhoon fighter jets and the Envoy IV CC1, which is making its flypast debut.
At the front of the flypast will be a Juno HT1 piloted by Flight Lieutenant Tom Knapp from 60 Squadron, No 1 Flying Training School based at RAF Shawbury. The event will end in a show of red, white and blue from the pilots of the Red Arrows.
