Trooping the Colour is kicking off the first of four days of celebrations for the Queen's Platinum Jubilee.
The event, which is the Queen's official birthday parade, is a military spectacle, involving more than 1,500 officers and soldiers and 350 horses from the Household Division.
It sees members of the Royal Family travelling in horse-drawn carriages from Buckingham Palace to Horse Guards Parade to watch the extravaganza before travelling back again.
And it usually ends with the royals then appearing on the balcony of Buckingham Palace as the RAF perform a special flypast overhead.
It's one of the rare times the whole of the Firm get together and over the years little snippets have been revealed over what goes on behind the scenes at the palace during the event.
And it seems many of the younger royals have a whale of a time of the event if sneak photos of them at the Palace are anything to go by.
In years gone by, Prince George, Princess Charlotte and Prince Louis have been too young to take part in a carriage ride from the palace to Horse Guards.
But snaps have shown them standing by the palace windows alongside their nanny pulling funny faces and squashing their noses against the glass as they look down at the crowds below.
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However, they did get their chance to experience the event later by joining their parents and the rest of the Firm on the balcony for the flypast.
Following the flypast, which in most years all members of the family enjoy, the royals are then thought to retreat inside for a get-together and drinks before heading their separate ways.
But as most parts of Buckingham Palace that the royals are in at Trooping the Colour are off limits - pictures of the big day behind the scenes hardly exist.
The only royal to break this seeming rule is Princess Eugenie who posted a photo on her personal Instagram page of her father Prince Andrew at the palace before Trooping the Colour in 2018.
But soon after Eugenie deleted the post after it was pointed out to her it was taken in a corridor in an area of the palace off limits to the public.
The image showed how the corridor was lined with marble busts and paintings including one depicting the wedding of Princess Maud of Wales, Queen Victoria's granddaughter.
The 28-year-old explained how she had struggled to choose a photo to celebrate the occasion, thinking a Balmoral snap would be 'too personal' and an Ascot photo 'too formal'.
She later told British Vogue: "I recently got in trouble for posting a picture of Papa in a corridor of the palace that was off-limits to the public."
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