Queen Elizabeth II marks her 90th birthday on Thursday as Britons and many throughout the world celebrate her long and dignified reign. She will celebrate again in June with national events to mark her official birthday.
Above: Visitors sit on a bench outside of Windsor Castle on April 20, 2016. Queen Elizabeth will celebrates her 90th birthday at the castle.
A passerby is reflected in a window display portraying Britain's Queen Elizabeth in Windsor on April 20.
Terry Hutt, a royal fan, stands in front of the castle in Windsor on April 20. Royal fans are gathering in Windsor ahead of Thursday's celebrations.
A British monarch celebrates his or her birthday twice a year, once on the actual day and once in early June, when the event can be marked with the gala Trooping the Color parade in central London. The June date is chosen in part because the famously fickle British weather just might produce a few sunny hours at that time of year. And the Buckingham Gardens are gloriously in bloom.
Workers install a new mural by Frederick Wimsett of Britain's Queen Elizabeth II in central London on April 19.
A royal fan adjusts her Union flag glasses in Windsor on April 20.
Giant terracotta busts of Britain's Queen Elizabeth and Prince Philip are displayed in the garden of Fifield House Farm near Windsor on April 20.
Britain's Queen Elizabeth II smiles as she is greeted by school children as she arrives to open a bandstand at Alexandra Gardens in Windsor on April 20. Queen Elizabeth II is set to celebrate her 90th birthday on April 21, with a family gathering and a cake baked by a reality television star, as a new poll finds Britain's longest serving monarch is as popular as ever. The queen has reigned for more than 63 years and shows no sign of retiring, even if she has in recent years passed on some of her duties to the younger royals.
A spectator takes photographs during the changing of the guard ceremony outside of Windsor Castle on April 19.
Royal fan John Loughrey poses outside Windsor Castle on April 19.
Bunting themed for Queen Elizabeth's birthday hangs in Windsor on April 19.
A handout image released in London on April 20 shows a Royal Mail postage stamp sheet that has been issued to mark the 90th birthday of Queen Elizabeth. The stamp sheet, made from a photograph taken in the White Drawing Room at Buckingham Palace in 2015, features four generations of the British Royal family, Britain's Prince Charles, Prince of Wales, Britain's Queen Elizabeth II, Britain's Prince George, and Britain's Prince William, Duke of Cambridge. Britain's postal service released a set of special stamps to mark the queen's birthday, including the first to feature her great-grandson, two-year-old Prince George.