In the immediate aftermath of 9/11, Queen Elizabeth II moved.
The British monarch broke tradition by showing solidarity with the nation two days after the 9/11 attacks.
The monarch ordered the Coldstream Guards to play "The Star-Spangled Banner" during the Changing of the Guard at Buckingham Palace in order to pay tribute to the lives that were lost on that tragic day.
A selection of music ranging from traditional marches to songs from musicals and familiar pop songs is usually performed by the band at the daily ceremony in front of Buckingham Palace.
There are live updates on Queen Elizabeth II's 70 year reign.
The Changing of the Guard is one of the most popular attractions in London.
Hundreds of Americans were among the 3000 people who gathered to hear the "The Star-Spangled Banner" perform.
Hundreds of people in the crowd sang along as the band of the Coldstream Guards began the US national anthem.
American citizen Laura Esposito told the Guardian that she wanted to be closer to home.
The prince was at the ceremony with his mom. William Farish was the U.S. ambassador to Britain at the time.
The monarch broke royal protocol again the next day to show her support for the U.S.
She attended a memorial service with her husband and son. She wiped away a tear as the thousands of church-goers who attended the service sang along with the "The Star-Spangled Banner" being played.
The monarch visited Ground Zero in New York City in 2010 for the first time since 1957.
During the Changing of the Guard, Queen Elizabeth once again asked that the American nation anthem be played.
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"As we mark the 20th anniversary of the terrible attacks on 11th September 2001, my thoughts and prayers - and those of my family and the entire nation - remain with the victims, survivors, and families affected," she said.
My visit to the site of the World Trade Center in 2010 is something I will remember for the rest of my life. We pay tribute to the resilience and determination of the communities who joined together to rebuild as we honor those who lost their lives.