The Royal Family's social media accounts shared a solo photo of the Queen to mark her 95th birthday.
The Monarch celebrates the landmark occasion just days after saying goodbye to her beloved husband, Prince Philip.
Alongside an old picture of the Queen wearing a purple hat and coat, they wrote: "Today is The Queen’s 95th birthday. HM was born on 21 April 1926 at 17 Bruton Street in London, the first child of The Duke and Duchess of York.
"This year The Queen remains at Windsor Castle during a period of Royal Mourning following the death of The Duke of Edinburgh."
Well-wishers took to the comments section to share messages of support to the Queen.
One wrote: "Your Majesty, Thinking of you today and to wish you as Happy a Birthday as is possible during this deeply sad time for you."
Another added: "Your Majesty, On the occasion of you Birthday please know that many people throughout the country and beyond share blessings of your life and achievements. Celebrations are not appropriate whilst you are in mourning for The Duke of Edinburgh so we wish you love and reflection."
A third commented: "Wishing you the Happiest possible day (under the circumstances).. Your Majesty continues to shine bright, even during your darkest hour."
The Queen will spend the day privately with visits from a few members of her family in Windsor.
Sophie Wessex, the Duchess of Cambridge and Princess Anne have reportedly drawn up a rota to ensure she isn't alone today.
It's likely that she'll also get to spend time with her new great-grandson August, as Princess Eugenie and her husband Jack are living just around the corner in Frogmore Cottage.
However Prince Harry has returned to the US to be reunited with Meghan Markle, who is heavily pregnant.
It's also likely that she will take her corgi puppies for a walk, and she's said to have found great comfort in the dogs since the Duke of Edinburgh's death.
The Queen's official birthday falls in June, however Trooping the Colour has been cancelled for the second year running due to Covid.
