Britain's Queen Elizabeth II (second from left); President Obama; Camilla, Duchess of Cornwall, who is Prince Charles' wife; first lady Michelle Obama; and Prince Philip, the queen's husband, take part in the official welcome ceremony outside Buckingham Palace with a honor guard from the Scots Guards at the start of the president's  state visit in London on Tuesday, May, 24, 2011. (AP Photo/Alastair Grant)

Photo by: Alastair Grant

Britain's Queen Elizabeth II (second from left); President Obama; Camilla, Duchess of Cornwall, who is Prince Charles' wife; first lady Michelle Obama; and Prince Philip, the queen's husband, take part in the official welcome ceremony outside Buckingham Palace with a honor guard from the Scots Guards at the start of the president's state visit in London on Tuesday, May, 24, 2011. (AP Photo/Alastair Grant)