Here's why the Queen has 2 birthdays

As celebrations for the Queen's 90th birthday begin, Brits and foreigners alike wonder why Her Majesty enjoys two birthdays each year.

The Queen has her actual birthday, on April 21, and an official birthday which is held on a Saturday in June (this year, her official celebration is on June 11) - it turns out, because of the weather.

Sovereigns whose real birthdays fall in colder months have often celebrated an official birthday on a different date in the hope of good weather for their birthday parade, known as the Trooping the Colour, according to the Royal Family's official website.

Because British weather can be cold on April 21, the Queen celebrates her official birthday in June.

For the Trooping the Colour, the Queen parades the streets of London - through Buckingham Palace, The Mall, and the Horse Guards Parade - and makes an appearance on the balcony of Buckingham Palace with other Royal Family members.

The elaborate parade dates back to 1660 during the Restoration of King Charles II and became an occasion for honouring both the monarch and the military in 1748, according to a blog post by the historian, author, and royal commentator Dr. Carolyn Harris.

The Trooping the Colour has been held on the sovereign's birthday since the traditions were combined by King Edward VII in 1901, Harris explained in her blog post. The King, whose birth date was in November, marked his official birthday in May or June, according to the Royal Family website.

Festivities for the Queen's actual birthday have already started with a visit to the Royal Mail's Windsor office and Alexandra Gardens. On April 21, Her Majesty will walk around Windsor, unveil a plaque on the Queen's Walkway, and light a beacon that will be followed by over 900 set alight across the UK and the world, a release from the Royal Family website explains.

Over her official birthday weekend (June 10-12), the Queen will attend a national service of Thanksgiving at St. Paul's Cathedral, a Patron's Lunch (where her patronage to over 600 organisations will be honoured), as well as the Trooping the Colour parade, of course.

Pubs in England and Wales will also stay open until 1 a.m. on June 10 and June 11 to celebrate.