It is the Queen's birthday celebration on Saturday 12 June - but she also has another one earlier in the year.
The Queen has two birthdays - her real one - on 21 April, as she was born on 21 April 1926 and turned 95 this year.
Then a second one - the official celebration - on the second Saturday of June.
So why does the Queen have two birthdays, and how does she celebrate them?
In the past, official celebrations to mark a King or Queen's birthday in the UK have been held on a day that isn't their actual birthday.
The Queen's great-grandfather, Edward VII, who was King from 1901 to 1910 was born in November, which is not known in the UK for its good weather.
But he wanted it to be possible to have a big public celebration - and November wasn't the time do it.
So, given that his actual birthday wouldn't be a good time of year for a birthday parade, he decided to combine it with an annual military parade in the summer, when the weather would hopefully be nice.
The Queen usually spends her actual birthday with her family.
There is usually a 41-gun salute in Hyde Park, a 21-gun salute in Windsor Great Park and a 62-gun salute at the Tower of London on 21 April but they were cancelled this year because of the coronavirus pandemic.
The Queen and the Royal Family were still in mourning following the death of Prince Philip, aged 99, so celebrations were private.
The Trooping the Colour parade marks her official birthday and usually takes place in June, but that has also been cancelled this year.
Following consultation with Government and other relevant parties it has been agreed that The Queen's Official Birthday Parade, also known as Trooping the Colour, will not go ahead this year in its traditional form in central London. Options for an alternative Parade, in the quadrangle at Windsor Castle, are being considered.
Trooping the Colour has marked the official birthday of the British monarch for more than 260 years.
It's also known as The Queen's Birthday Parade.
More than 1400 soldiers, 200 horses and 400 musicians usually take part in the event, so it's quite a spectacle!
Lots of members of the public waving flags and wearing Union Jacks normally fill the Mall outside Buckingham Palace to watch it.
On the day, normally a big parade starts at the Queen's official residence - Buckingham Palace - before moving along the Mall to Horse Guards Parade at Whitehall, near to Downing Street, and then back again.
Then it's traditional for the royal family to travel down the Mall as part of the ceremony, and gather on Buckingham Palace's balcony to greet well-wishers and watch RAF planes perform an aerial display for the occasion.
In 2021 however, the celebration will look similar to last year's scaled down Trooping the Colour with the notable difference that, after Prince Philip's death, the Queen will be accompanied by her cousin, the Duke of Kent.
There will still be a parade to accompany the Queen to Horse Guards and Her Majesty will be greeted by Royal Salutes, and the National Anthem.
This year, the parade will also be "formed by soldiers who have played an integral role in the NHS COVID-19 response, as well as those who have been serving on military operations overseas."
There will also be a 41 Gun Royal Salute at Windsor Castle.