The Queen has celebrated her 90th birthday by greeting huge crowds of well-wishers outside Windsor Castle.

Celebrations are taking place across the UK in honour of the longest-serving monarch.

Here's how the nation marked the milestone.

  • Queen meets well-wishers

The Queen smiles as she greets crowds. Credit: PA Wire

The Queen greeted well-wishers during a walk-about outside Windsor Castle.

Royal fans cheered the monarch as she stepped from her car in front of the Henry VIII gate.

She was given flowers and cards as she walked through the town accompanied by her husband the Duke of Edinburgh.

Royal enthusiasts singing happy birthday to the Queen couldn't come to a consensus on what to call her.

Half of the crowd appeared to chant "happy birthday Mrs Windsor" while others appeared to call her "the Queen".

Fans then erupted in laughter as they realised the gaffe.

The Queen also cut her birthday cake made by Great British Bake Off winner Nadiya Hussain.

Hussain - who confessed she was "super nervous" about the prospect of baking for the longest-reigning monarch - showed her Majesty the three-tier orange drizzle before singing Happy Birthday.

It was a walkabout which also turned into a royal drive-by, when the Queen delighted the crowds by travelling standing up in a review car.

  • Gun salutes fired

The King's Troop Royal Horse Artillery perform a gun salute in Hyde Park. Credit: PA Wire

Gun salutes were also fired from Edinburgh and Stirling castles and in London's Hyde Park.

  • PM leads tributes

David Cameron paid tribute to the Queen in the Commons

David Cameron has wished the Queen "health and happiness" on her 90th birthday as he paid tribute to her "extraordinary service".

"We are uniquely blessed in our country. Her Majesty's service is extraordinary and it is a joy for us all to celebrate, to cherish and to honour."

Jeremy Corbyn also joked that the Queen could be an Arsenal fan, while also wishing her a happy birthday.

  • This evening's events

Westminster Palace will be lit red, white and blue for the special royal anniversary from the evening until dawn on Friday.

At about 7pm, The Queen will light the principal beacon to celebrate her birthday, which will set in train a series of over a thousand beacons across the country and worldwide.

A series of lighting events throughout the country will create a network of flames in celebration.

  • Family photographs released

A photograph of the Queen surrounded by her five great-grandchildren and her two youngest grandchildren has been released.

Three pictures giving an insight into the Queen's family life were released to mark the occasion.

She is surrounded by her five great-grandchildren and her two youngest grandchildren in one of the images.

The Queen is also pictured with her corgis and dorgis, and in a third picture with her only daughter the Princess Royal.

The Queen is pictured sitting on the sofa with her only daughter, Princess Anne.
The third picture captures the Queen walking in the private grounds of Windsor Castle with her dogs.