Puppeteers from the acclaimed stage show Warhorse have taken position on the grass verge of Windsor Castle to meet the Queen once more. 

Her Majesty saw the National Theatre performance in 2009, and met Joey the horse again in 2013. 

Joey stood proud on top of the National Theatre in London to welcome the Queen as she travelled down the Thames during the Jubilee Pageant in 2012. 

Lord William Waldegrave, provost of Eton College, spoke to the BBC about the Queen's long history in Windsor. 

Her Majesty, along with Princess Margaret, received private tuition from history teacher Sir Henry Marten at the all-boys public school. 

Sir Henry was not used to teaching girls, and would greet the two princesses by saying, "Gentlemen, open your books."

Prince Charles has paid tribute to his mother on her 90th birthday with a special radio broadcast, in which he read an edited passage from William Shakespeare's Henry VIII.

To listen to this, click here. 

Image source, AP

Royal fans - with varying fashion statements - have been out early to stake prime positions ahead of the Queen being out and about in Windsor.  

She is due to unveil a plaque for a digital walking trail before taking part in a walkabout around the Berkshire town.  

Well-wishers have come from far and wide to take part in the celebrations. 

Canadian Margaret has travelled an impressive 3,500 miles just to see the Queen on this historic occasion. 

She said: "The Queen's special to us in Canada. I was in Windsor a decade ago for her 80th, and now I'm here a decade later for her 90th."

Hundreds of people were already gathering in Windsor in the early hours ahead of the Queen's birthday walkabout in Windsor later. 

Some members of the public camped out overnight to get a prime spot to catch a glimpse of Her Majesty on her 90th birthday. 

Image source, AP

Good morning and welcome to our live page.

It is the Queen’s 90th birthday today and celebrations get under way later as she takes part in a walkabout in Windsor. 

Accompanied by the Duke of Edinburgh, she will unveil a plaque marking The Queen’s Walkway - a 6.3km trail that links 63 significant points in the Berkshire town.

The trail was designed to recognise the moment the monarch broke the record – on 9 September last year – held by her great-great-grandmother Queen Victoria by being on the throne for 63 years and seven months.

Image source, AFP/Getty

The Queen's day of engagements saw her entertained by hundreds of schoolchildren performing songs including When I'm 64 - to mark her 64 years on the throne. 

Mark Taylor, head of libraries, arts and heritage for the Royal Borough of Windsor and Maidenhead accompanied the Queen on her trip to Alexandra Gardens, and said: "She did enjoy that song". 

He said she was also pleased with the weather, saying: "We're so lucky to have a sunny day."

She will be hoping the sun stays shining for her walkabout in Windsor tomorrow - her actual birthday. 

We're pausing our live coverage here but will continue on Thursday. 

Jeremy Corbyn, a lifelong republican, has said he is "looking forward" to wishing the Queen a happy birthday. 

The issue was raised at PMQs by Conservative MP Nigel Adams ahead of a celebratory debate in the House of Commons, prompting Prime Minister David Cameron to reply: 

Corbyn then said - to laughter from fellow MPs: "I am also looking forward to wishing her a happy birthday tomorrow." 

BBC iWonder

• The Queen has been married for 68 years, longer than any other British monarch 
• Her coronation was the first to be televised and was watched by over 20 million people in the UK
• There have been 12 UK prime ministers, seven Archbishops of Canterbury and seven Popes during her reign
• She has sat for more than 130 official portrait paintings
• During her reign, she has visited 117 countries, travelling more than a million miles
• In 2012 she became the second British monarch to celebrate a diamond jubilee, and in 2015 became the UK's longest reigning monarch 

BBC iWonder has a comprehensive timeline of the Queen's life for an in-depth look at her reign. 

Read more.

Here are some of the images from the Queen's two engagements today. 

She shared a joke with postmen - apparently about their shorts - before Royal Mail chief executive Moya Greene showed her an exhibition at the delivery office. 

It was then a short trip to Alexandra Gardens where she was greeted by local schoolchildren. 

The Queen, accompanied by the Duke of Edinburgh, listened to them singing before opening a bandstand.

Image source, Reuters

Image source, Reuters

Image source, AFP/Getty

Image source, Getty Images

Image source, Getty Images

When she was at the Royal Mail delivery office in Windsor earlier, the Queen joked that she may have added to their post bags.

While meeting staff at the Windsor depot, which has been renamed the Queen Elizabeth delivery office in her honour, she suggested to Royal Mail Group chief executive Moya Greene that cards and gifts from well-wishers may have added to the huge number of items they deliver every year.

On Thursday, she becomes Britain's first nonagenarian monarch. 

Alex Morrison
BBC News reporter

Image source, Getty Images

"The actual Queen?"

Those were the words on the lips of many Windsor tourists on learning that the Queen had two engagements in the town today.

Many were excited. Two of the visitors had watched hours of coverage from their home in the US and said it would be "great" to see her in person.

And they soon joined the crowds jostling to see the UK's longest-reigning monarch.

Getting a good view became serious business, especially for parents whose children could not see.

"When the Queen gets here I'll lift you up. Is that a deal?" one mum told her toddler - more than an hour before the scheduled arrival.

But in the end everyone seemed satisfied with a brief glimpse.

In the words of one teenage girl as the royal car passed almost within touching distance: "Oh my God, I can't believe it. She's so close."

The Queen and Duke of Edinburgh have returned to Windsor Castle following today's engagements. 

On Thursday, she will go on a walkabout in the town centre to meet the crowds before unveiling a plaque marking The Queen's Walkway, a 6.3km walking trail through Windsor.

Later in the day, she will light the first in a chain of more than 1,000 beacons being lit across the world to mark her birthday.

Prince Charles is hosting a private family dinner at the castle on Thursday evening. 

Prince William has paid tribute to the Queen, saying she has been a "guiding example" of what a good monarch should be. In a BBC interview, he also answered criticism of his commitment to royal duties, which has seen him being referred to as "workshy William" in a number of newspapers, saying he is willing to take on more responsibility when the time comes. "I take duty very seriously. I take my responsibilities very seriously," he said.

Watch the full interview here.

Image source, PA

One of the most unusual tributes to the Queen as she turns 90 has to be this terracotta head in her likeness. 

The 12ft head stands next to one representing the Duke of Edinburgh in the front garden of Ben Bennett's home in Oakley Green, just outside Windsor. 

The heads, which have plastic grass hair, were discovered by Mr Bennett, 83, at a house clearance in Chelsea.

He says he has been "flooded with visitors" coming to see them.  

Image source, PA