Queen Elizabeth II (Photo Credit: gov.uk)

On April 21, throngs of people lined along the street of Windsor to get a glimpse of the world's favorite monarch, Queen Elizabeth II, on her milestone 90th birthday. They were not disappointed.

Dressed in a bright lime-green coat dress and hat, the beaming birthday "girl" mingled with the crowds, accepting bouquets of carnations (her favorite flower) and cards. She even smiled gracefully as the fans cheekily sang, "Happy Birthday, dear Queenie.” This, of course, was one of the many celebrations the sprightly 90-year-old and her husband, the 94-year-old Duke of Edinburgh, participated in that day.

And there are more parties to come. That's because thanks to a centuries-old tradition, British monarchs get to celebrate their birthdays twice - Once on the day when he or she is born and the other in June. Why? Simply because the weather is much nicer! So stay tuned for Queen Elizabeth II's summer birthday celebration on June 11!

Resources: washingtonpost,com, telegraph.co,uk, the dailybeast.com