Every June, there is a public celebration of the Queen's birthday called Trooping the Colour.
This year, it will take place on Saturday 8 June.
Her actual birthday is back in April, but Trooping the Colour has marked the official birthday of the British monarch for over 260 years.
Many members of the Royal family will attend the event, and it will be Prince Louis' first Trooping of the Colour.
But why is it called this and what happens when it takes place? Read on for everything you need to know.
Trooping the Colour is a military parade - so the name has a military background, which goes all the way back to the 17th Century.
It is a ceremony performed by more than 1,400 parading soldiers, 200 horses and 400 musicians, who come together each June in one of the most esteemed military displays in the world.
The guards which take part in the parade form one of the oldest regiments of the British Army - the Household Division.
They are like the Queen's bodyguards or personal troops, and have been part of the monarchy since the English Civil War ended in 1660.
'Colours' was the name given to the flags representing the different regiments in the British Army.
The flags all looked different, depending on the colours and symbols of each regiment.
The army used these flags so that soldiers could easily spot their unit when they were on the battlefield, because it used to be quite easy to get lost in battle.
Keeping an eye out for their own regiment's 'colours' was an easy way to keep everyone together.
Because of this, it was important that soldiers knew which colours belonged to which regiment, so they needed to be regularly displayed.
To do this, officers would march up and down in front of the troops (this is called 'trooping'), waving their flags (or 'colours'), so everyone could see which flags belonged to which regiment.
This is where the name 'Trooping the colour' comes from, when the colours of the different regiments of the British army were displayed.
Each year at Trooping the Colour, a different regiment's colours are trooped.
For the 2018 celebrations, it was the colours of the 1st Battalion Coldstream Guards, and in 2019, the colour will be trooped by 1st Battalion Grenadier Guards.
The Trooping the Colour parade officially begins when the Queen leaves Buckingham Palace in a carriage.
Until 1987, she actually used to make this journey riding side-saddle on a horse, dressed in the colours being trooped that year.
She travels down the Mall in front of crowds towards Horse Guards Parade at Whitehall, near to Downing Street.
When the Queen gets there, she is greeted by a royal salute from the soldiers on parade, before inspecting the troops.
Then, the 'colours' being trooped will be carried down the ranks and showed to the soldiers, just as the officers used to do in the past.
The Queen then leads the troops back down the Mall to Buckingham Palace for a second salute, and the official 'trooping' is over.
She has done this ceremony every single year since becoming Queen, apart from in 1955 when there was a rail strike.
Once this is done, she is joined by other members of the royal family on Buckingham Palace's famous balcony.
There is a special 41-gun salute in Green Park, just next to the palace, and a special aerobatic display by the RAF's display team, the Red Arrows.
Trooping the Colour takes place on 8 June 2019