Queen Elizabeth II Becomes Britain's Longest-Reigning Monarch

(nbcnews.com) 09/09/15 LONDON — Queen Elizabeth II is the longest-reigning monarch in British history, overtaking her great-great grandmother Queen Victoria's record of 63 years and 216 days on Wednesday.

Despite the milestone, it was business as usual for the 89-year old and her husband Prince Philip.

The queen formally reopened a restored railway line in Scotland where she offered rare remarks to jubilant crowds, touching only briefly on the significance of the day.

"Prince Philip and I are very grateful for the warmth of your welcome," she told the crowd. "Many ... have also kindly noted another significance attaching to today, although it is not one to which I have ever aspired. Inevitably, a long life can pass by many milestones. Mine is no different. But I thank you all and the many others at home and overseas for you touching messages of great kindness."

The queen was 25 when she succeeded her father King George VI after his death in 1952. There have been 12 British prime ministers — starting with Winston Churchill — and 12 U.S. presidents during her time on the throne.

She surpassed Victoria at around 5:30 p.m. local time (12:30 p.m. ET).

Tributes poured in from around the world led by British Prime Minister David Cameron who praised the queen as "a rock of stability in a world of constant change."

In a speech delivered to parliament on Wednesday, Cameron added: "It is of course typical of her selfless sense of service that she would have us treat this day like any other. While I rarely advocate disobeying her majesty, I do think it is right that today we should stop and take a moment as a nation to mark this historic milestone."

According to Cameron, the Queen has answered 3.5 million pieces of correspondence and sent 100,000 telegrams to centenarians across the Commonwealth.

She is also the country's best-traveled monarch, having undertaken 265 official visits to 116 countries.

"We couldn't be more proud of her," Cameron said. "She has served this country with unerring grace, dignity and decency. And long may she continue to do so."