The four-day Platinum Jubilee celebrations will kick off on Thursday with Trooping the Colour, the historic ceremony that celebrates the Queen's official birthday.

While the Queen's actual birthday is on 21 April, a second celebration also takes place later in the year. Normally it is held on the second Saturday in June, but it has been brought forward in 2022 to herald 70 years of the Queen's reign.

Yahoo News UK explains why the Queen has two birthdays, when the tradition started, and what actually happens on one of the most high-profile events on the royal calendar.

When is the Queen's real birthday?

Elizabeth II was born on 21 April 1926, the oldest daughter of the Duke and Duchess of York, who became King George VI and Queen Elizabeth when her uncle abdicated the throne.

In 2020 and 2021 the Queen has been in Windsor for her birthday. She is often in Windsor at this time of year for Easter Court but in the two years of coronavirus restrictions, there have been fewer official elements of this period in the royal calendar.

She reportedly spent her 94th birthday in 2020 video calling her family members. Her 95th birthday was spent in mourning, as it came just four days after the funeral of Prince Philip.

Her birthday has been marked privately for several years, and 2021 saw no official confirmation of any activities. It was reported she had a quiet lunch with family.

One of the biggest parts of the Queen’s birthday celebration is usually a series of gun salutes in three places.

In London, a 41 gun salute is performed in Hyde Park, and a 62 gun salute at the Tower of London.

Closer to her Berkshire home, a 21 gun salute is normally held at Windsor Great Park.

A basic gun salute is 21 guns, and 20 are added if the salute takes place in a royal park, which is why it’s 41 guns in Hyde Park.

They are traditionally fired at 10 second intervals by the King’s Troop Royal Horse Artillery, a mounted ceremonial battery.

Read more: Easter Court: Why does the Queen go to Windsor and what does she do at Easter?

The Queen also gets gun salutes for her official birthday and her coronation day. They’re also fired for various events like royal births or for heads of state visiting.

There were no gun salutes in 2020 or the first part of 2021 due to the pandemic. They were reinstated after the death of Prince Philip on 9 April, but there were none for the Queen's real birthday.

The monarch's official birthday

The practice of an official birthday for the monarch dates back 260 years, when George II repurposed the traditional Trooping the Colour for his own celebration.

George II’s actual birthday was in November, and the monarch was fed up with terrible British weather putting a dampener on any plans.

So he decided to combine his birthday with the Trooping the Colour, a military procession which was held every year and already a fixture of the British calendar.

Queen Elizabeth II’s father, King George VI, had his official birthday on the second Thursday in June, and the Queen adopted this for a few years after she acceded.

But in 1959, she decided to change it to the second Saturday in June.

It just so happens that her official birthday isn’t too far away from her coronation day, but the two aren’t linked.

What is Trooping the Colour?

Trooping the Colour involves more than 1,400 parading soldiers, 200 horses and 400 musicians, who perform with military precision.

The parade moves between Buckingham Palace, The Mall and Horseguards’ Parade.

It’s also the time of year we get the famous balcony pictures as all the Royal Family waves to the crowds and watches the RAF flypast, which marks the end of the event.

The Queen used to ride on horseback with the parade to carry out the inspection but now arrives by carriage.

She is greeted by a royal salute and carries out an inspection of the troops, operational soldiers wearing their ceremonial uniform of red tunics and bearskin hats.

After the bands have performed, the Regimental Colour, or flag, is processed, or trooped, down the line of soldiers.

Read more: Best photos of the Royal Family at Trooping the Colour through the years

The Household Division’s website explains: “Regimental flags of the British Army were historically described as ‘Colours’ because they displayed the uniform Colours and insignia worn by the soldiers of different units.

“If Troops were to know what their Regiment’s Colours looked like, it was necessary to display them regularly.

“The way in which this was done was for young officers to march in between the ranks of troops formed up in lines with the Colours held high.

“This is the origin of the word ‘trooping’.”

In 2020 and 2021, the ceremony has been downsized to match the coronavirus restrictions in place.

In 2020, the Queen viewed a small ceremony at the Quadrangle of Windsor Castle. She did not have any family members with her, just a couple of her aides.

Soldiers from the Welsh Guards and musicians from the Massed Band of the Household Division marched from the parade area, outside the Chapel, to the quadrangle.

While the parade was meticulously planned to ensure there were no places for the public to gather and watch, castle staff could be spotted peering out of windows to watch.