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Prince Charles and Camilla, Duchess of Cornwall, walk through a ticket gate as they prepare to travel on a Metropolitan underground train from Farringdon to King's Cross as they mark 150 years of London Underground on Jan. 30, 2013, in London.
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Prince Charles laughs as he prepares to travel on a Metropolitan underground train at Farringdon station as he and Camilla, Duchess of Cornwall, (not pictured) mark 150 years of London Underground on Jan. 30, 2013, in London.
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Prince Charles and Camilla, Duchess of Cornwall, prepare to travel on a Metropolitan underground train at Farringdon Station as they mark 150 years of London Underground on Jan. 30, 2013, in London.
Chris Jackson - WPA Pool/Getty Images
Camilla, Duchess of Cornwall, and Prince Charles travel on a Metropolitan underground train from Farringdon to King's Cross as they mark 150 years of London Underground on Jan. 30, 2013, in London.
Chris Jackson - WPA Pool/Getty Images
Camilla, Duchess of Cornwall, and Prince Charles travel on a Metropolitan underground train from Farringdon to King's Cross as they mark 150 years of London Underground on Jan. 30, 2013, in London.
Chris Jackson - WPA Pool/Getty Images
Camilla, Duchess of Cornwall, and Prince Charles travel on a Metropolitan underground train from Farringdon to King's Cross as they mark 150 years of London Underground on Jan. 30, 2013, in London.
Chris Jackson - WPA Pool/Getty Images
Camilla, Duchess of Cornwall, and Prince Charles travel on a Metropolitan underground train from Farringdon to King's Cross as they mark 150 years of London Underground on Jan. 30, 2013, in London.
Chris Jackson - WPA Pool/Getty Images
Camilla, Duchess of Cornwall, and Prince Charles travel on a Metropolitan underground train from Farringdon to King's Cross as they mark 150 years of London Underground on Jan. 30, 2013, in London.
Chris Jackson/Getty Images
Camilla, Duchess of Cornwall and Prince Charles visit platform 9 3/4 at King's Cross Rail Station during a visit to mark 150 years of London Underground on Jan. 30, 2013, in London.
Chris Jackson/Getty Images
Prince Charles and Camilla, Duchess of Cornwall, visit platform 9 3/4 at King's Cross Rail Station during a visit to mark 150 years of London Underground on Jan. 30, 2013, in London.
Chris Jackson/Getty Images
Prince Charles and Camilla, Duchess of Cornwall, visit Platform 9 3/4 at King's Cross Rail Station during a visit to mark 150 years of London Underground on Jan. 30, 2013, in London.
Chris Jackson/Getty Images
Camilla, Duchess of Cornwall, and Prince Charles visit Platform 9 3/4 at King's Cross Rail Station during a visit to mark 150 years of London Underground on Jan. 30, 2013, in London.
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Camilla, Duchess of Cornwall, and Prince Charles, second right, study a model of the refurbished King's Cross Rail Station during a visit to the terminal as they mark 150 years of London Underground on Jan. 30, 2013, in London.
John Stillwell - WPA Pool/Getty Images
Camilla, Duchess of Cornwall, and Prince Charles study a model of the refurbished King's Cross Rail Station during a visit to the terminal as they mark 150 years of London Underground on Jan. 30, 2013, in London.