In 1952 the woman known today as Queen Elizabeth II was just Elizabeth, a 25-year-old member of England's royal family visiting a remote village in Kenya.
When word came on Feb. 6 of that year that her father, George VI, had died, Elizabeth cut her trip short and flew home to London. She was greeted at the airport by her country's then-Prime Minister Winston Churchill and she was crowned Queen Elizabeth II.
Today, 60 years later, the 85-year-old Queen marked her Diamond Jubilee anniversary with a message thanking the British people for their support, and pledging to continue her dedication to serving them and people around the world.
"I am writing to thank you for the wonderful support and encouragement that you have given to me and Prince Philip over these years," she wrote today in a message to the nation, which was released by Buckingham Palace. "In this special year, as I dedicate myself anew to your service, I hope that we will all be reminded of the power of togetherness and the convening strength of family, friendship and good neighborliness, examples of which I have been fortunate to see throughout my reign."
The anniversary makes Queen Elizabeth, already Britain's oldest serving monarch, the country's longest-serving monarch after Queen Victoria, who reigned for more than 63 years. The queen, mother to four and grandmother to eight, has now outlasted 11 U.S. presidents.
"Queen Elizabeth II rates among the best, in fact, better than the best," Dickie Arbiter, former press secretary to the Queen, told ABC News.
"The queen doesn't change. The queen adapts, and that's why it survives," he said of the monarch.
Celebrations of her Diamond Jubilee officially begin today when the queen and Philip, 90, visit a nursery school and the town hall in the town of King's Lynn.
The celebrations will continue throughout the year as members of the royal family - from Prince Charles to Prince William and Kate Middleton - travel around the world to take part in ceremonies and events honoring the queen. The queen herself and Philip, also known as the Duke of Edinburgh, will embark on a tour of England in March.
The main event, the 2012 Diamond Jubilee weekend, will be held in June and feature a star-studded concert and boat pageant on the Thames river with a 1,000-strong flotilla.
The Palace also today released a special set of portraits of the queen and Philip, taken by John Swannell in the Centre Room at Buckingham Palace last December, to mark the Jubilee. Two new photographs of the queen, wearing the same necklace Queen Victoria wore in her own Diamond Jubilee portrait in 1897, were also released.
ABC News' Nick Watt contributed to this report.