At noon, a 41-gun salute was fired by The King's Troop, Royal Horse Artillery, in Hyde Park, close to Buckingham Palace.

Earlier, a tweet from the Royal Family account shared a black and white picture of the monarch aged two, taken in 1928.

Back then, the message reads, "it was never expected she would be Queen, and this year Her Majesty is celebrating her #PlatinumJubilee - a first in British history".

The Duke and Duchess of Cambridge also tweeted two pictures, one of the couple with Her Majesty at the Chelsea Flower Show a few years ago and another of the Queen and Prince Philip surrounded by their great-grandchildren.

An inspiration

Calling the Queen "an inspiration", they wrote: "Wishing Her Majesty The Queen a very happy 96th birthday today!"

The Prince of Wales and his wife, Camilla, Duchess of Cornwall, also posted on Twitter.

They wished her "a particularly special 96th birthday" alongside various pictures including one of Charles kissing his mother's hand.

Her Majesty is set to spend the day at Sandringham, the Norfolk estate where she enjoyed family gatherings with the Duke of Edinburgh, her late husband.

To mark the occasion, the Royal Windsor Horse Show released an image of the monarch taken last month at Windsor Castle.

In it, the Queen is flanked by two ponies, called Bybeck Nightingale and Bybeck Katie, that will both take part in the show's tribute to the monarch.

The Changing of the Guard went ahead as usual at 11.00am, but it took place at Windsor Castle rather than Buckingham Palace to mark the day.

Large crowds, enjoying glorious spring sunshine, gathered to watch as the Band of the Coldstream Guards played Happy Birthday.

Read more:
• Queen says she was left 'very tired and exhausted' during her bout of COVID-19
• Mark your calendars - here are the plans for Queen's Platinum Jubilee celebrations
• How you can get tickets to jubilee Buckingham Palace concert

A busy Easter

The Queen's birthday comes after an eventful Easter break during which she was visited by the Duke and Duchess of Sussex.

Harry said his grandmother was "on great form" when they met before he and wife Meghan travelled to the Netherlands for the Invictus Games.

Speaking to NBC's Today show, he said he wanted to make sure she was "protected" and had "the right people around her".

It is thought the monarch will stay at the Duke of Edinburgh's cottage Wood Farm while at Sandringham, a property she said her late husband "loved" as "sea was so close".

The Queen spoke about the cottage on the property when she hosted a rare public event at Sandringham on 5 February, the eve of her Platinum Jubilee.

Teresa Thompson, 70, the retired housekeeper of Wood Farm, said after speaking to the Queen that day: "All the Royal Family love Wood Farm, because it's out of the way, it's small, it's intimate.

"You haven't got lots of officials, it's just the close staff.

"And they literally can relax in the family house, it's wonderful, and I had a wonderful 22 years down there, it was the best time of my life without a doubt."

The Queen's 96th birthday has also been marked by Barbie, with the toy brand releasing a limited-edition doll of the monarch.

The Queen has also received birthday wishes from Prime Minister Boris Johnson and Labour leader Sir Keir Starmer.