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.
