Queen Elizabeth doesn't sing the U.K.'s national anthem, or any other national anthem, in public. But following the 9/11 attacks, the monarch did away with protocol and tradition and reportedly sang "The Star-Spangled Banner" at one private event.

Her Majesty attended the memorial services for the victims at the St Paul's Cathedral in London the day after the tragic attack in America. She was with the royal family and some officials of the U.K. government, including Prime Minister Tony Blair and U.S. ambassador to Britain, William Farish. 

According to reports, Queen Elizabeth joined in the singing of the U.S. National Anthem and was seen wiping a tear from her eye. For the first time, Her Majesty also permitted the playing of "The Star Spangled Banner" during the Changing of the Guards on Sept. 12, 2001.  

Some 5,000 Americans, who were living in London at that time, watched the ceremony in tears. Some had their right hand over their hearts, as a salute and gesture of patriotism. 

One American bystander, Jenny Lee from San Francisco, said that she appreciated the Queen's gesture. The woman said she feels that Britain was one with the Americans and it made her feel better even as she is miles away from home.

The British people also people condoled with the Americans by visiting the U.S. embassy at the Grosvenor Square. According to The Guardian, the first person to sign the book for condolences was Prince Charles

Ten years after the 9/11, Queen Elizabeth, along with Prince Philip, made a rare visit to New York City and placed a wreath on one of the memorials on Ground Zero. She especially memorialized the British citizens who also died at the attack. 

The Queen, through the British Memorial Garden Trust, also commissioned a small garden in New York City's financial district for the 67 British victims. The garden has 67 bamboo shrubs that supposedly flourish during the colder months of the year. It also has a planting bed filled with Magnolia "Elizabeth." One of the first plants of this species was set by Prince Harry during his visit to New York in 2009.

The Queen Elizabeth II Garden in Hanover Square, which actually opened in 2008, is still well-maintained amid this pandemic crisis. Before the public health crisis, various events took place at the garden, including the annual memorials to the victims.