The UK's longest-serving monarch will celebrate her 90th birthday this week, with events taking place across Britain to mark the occasion. Queen Elizabeth II was born on 21 April 1926 at her maternal grandfather's house in Mayfair, London.

Although Thursday marks the Queen's actual birthday, she has a second "official" birthday on a Saturday in June. Traditionally, official celebrations to mark a sovereign's birthday have been held on a day other than their actual date of birth, particularly when the actual birthday has not fallen in the summer. This year, Queen Elizabeth's second birthday – the official, but not actual birthday – will be celebrated on 11 June.

Here are some of the events taking place over April, May and June to celebrate the Queen's two birthdays.

21 April

On her actual birthday, the Queen will unveil a plaque marking the start of a four-mile Queen's Walkway at the bottom of Castle Hill in Windsor. Afterwards, the Queen and Duke of Edinburgh will greet members of the public, but you will need to get there early to get a good place.

At 2.30pm, the Royal Borough of Windsor will hold its traditional 21-gun salute on the Long Walk near the Brook Street entrance. On Thursday evening, the Queen, along with the Duke of Edinburgh, the Prince of Wales and the Duchess of Cornwall, will light a beacon in Windsor at around 7pm. More than 1,000 beacons across the country and worldwide will be lit.

12 - 15 May

The Queen's 90th birthday celebration event will take place over four nights from 12 to 15 May in Home Park Private, Windsor Castle. Members of the royal family will attend each night, including the Queen who will be there for the final night of the celebrations.

Trooping the Colour
Trooping the Colour – Queen Elizabeth II\'s Birthday Parade – at The Royal Horseguards in June 2014 Chris Jackson/Getty

The non-profit event will raise money for charities. Kylie Minogue, Katherine Jenkins and Jess Glynne are set to perform on the final night of the celebrations, which will be aired by ITV.

10 June

The Queen and The Duke of Edinburgh will attend a National Service of Thanksgiving at St Paul's Cathedral. The Duke of Edinburgh will turn 95 on this day, but has said he does not want any public celebrations.

11 June

The Queen will attend her birthday parade on her official birthday along with members of the royal family on Horse Guards Parade. This parade is called the Trooping the Colour – the official annual celebration of the Queen's birthday. It will be televised by the BBC from 10am.

What is Trooping the Colour?

According to the royal websites, the parade is an annual event: "Over 1,400 parading soldiers, 200 horses and 400 musicians come together each June in a great display of military precision, horsemanship and fanfare to mark the Queen's official birthday.

"The streets are lined with crowds waving flags as the parade moves from Buckingham Palace and down The Mall to Horse Guard's Parade, alongside members of the royal family on horseback and in carriages. The display closes with an RAF fly-past, watched by members of the royal family from Buckingham Palace balcony."

12 June

The Queen will attend the patron's lunch, a celebration of her patronage of more than 600 organisations in the UK and around the Commonwealth since 1952. A giant picnic will take place at The Mall in London, with entertainment from street performers.