Mark, from Leighton Buzzard in Buckinghamshire, emails:

Dan Wolpert, from the US, emails:

Anja, from Slovenia, emails:

Daily Mail journalist and biographer Robert Hardman spoke to Anne Diamond about how the Queen continues to be so active at the age of 90. 

He said that a former private secretary said - lovingly - that "the Queen is as strong as a yak" due to good health, strong faith and Prince Philip. 

House of Commons
Parliament

Labour leader Jeremy Corbyn continued the tributes to the Queen. 

He said: "I admire her energy and wish her well in her continuing and outstanding commitment to public life - I wish her a very happy 90th birthday."  

House of Commons
Parliament

The Prime Minister opened the Commons debate by telling MPs that comprehending the scale of the Queen's public service is "truly humbling".

He listed some of her achievements, including meeting a quarter of all American presidents and advising 12 prime ministers.

The Prime Minister admitted to testing her patience, but denied that he had ever sent her to sleep by "droning on about Europe", as was depicted in the play The Audience. 

Multiple regiments will be in Windsor to perform for the Queen, and the crowds which are expected to reach the thousands. 

Senior director of music Lieutenant Colonel Kevin Roberts told BBC Berkshire what preparation goes into preparing for such an important event. 

David Cameron has paid tribute to the Queen in the Commons.  

The prime minister said no other country had a head of state "with such wisdom and patience". 

He said when people meet the Queen "they remember it for the rest of their lives". 

Crowds in Windsor continue to grow larger ahead of the Queen's public appearance in the town later. 

The monarch will soon appear to unveil a plaque for a digital walkway before she carries out a walkabout of the town. 

The Coldstream Guards - the oldest regiment in the British Army in continuous service - has begun parading through Windsor. 

The band is providing royal accompaniment to the birthday walkabout. 

Image source, PA

Image source, PA

The Queen's residency Holyroodhouse is marking her 90th birthday by hosting the first of three special exhibitions showcasing outfits from the Queen's childhood to the present day.  

Celebrations are being organised in many parts of Scotland to mark the occasion. 

To read more about how Scotland is celebrating, click here.  

Crowds have been getting creative with their appearances to help celebrate the Queen's 90th birthday.

Some have been camping out overnight - not long to go now before the Queen makes an appearance in the town. 

Image source, Reuters

Image source, PA

Image source, PA

Former royal press secretary Dickie Arbiter speaks to the BBC's Andrew Peach on why Windsor Castle is so special to the Queen. 

He said that the royal residence held a lot of special memories for the Queen, including growing up with her father and mother. 

Reality TV star Joey Essex has come to Windsor for the Queen's birthday walkabout, and the BBC's Susanne Courtney tested his knowledge with a royal quiz. 

When asked to name another monarch who had served more than 50 years, he said: "Churchill". 

Image source, EPA

Royal gun salutes will be fired from each of the UK's capital cities and at other authorised stations across the UK later.

Most of the salutes will be 21 guns in length - the standard royal gun salute - and will be held at locations including Hillsborough Castle, Cardiff Castle, and Edinburgh Castle.

In London, the King's Troop Royal Horse Artillery will stage a 41-gun salute at noon in Hyde Park. 

And the Honourable Artillery Company will fire a 62-gun salute across the Thames from the Tower of London at 13:00 BST.

Three town criers from Chelmsford have come to Windsor to wish the Queen a very happy birthday. 

No microphone will be required.