Today's journey was the first ever joint tube trip for Prince Charles and the Duchess of Cornwall.
Although both of them now qualify for an over-60s Freedom Pass, they were presented with commemorative Oyster cards topped up with £10 credit for the one stop journey from Farringdon to King's Cross.
A brand new train was used, which arrived at the platform empty. But members of the public boarded along with the royal couple - separated only by a group of policemen standing further down the carriage.
When the royal couple arrived at King's Cross they were taken to "Platform nine and three quarters", a Harry-Potter themed attraction in the station.
In the books by JK Rowling, the "Hogwarts Express" steam train leaves from a secret platform, which witches and wizards reach by pushing a trolley through a wall.
But Charles and Camilla remained firmly in the land of the "muggles" or non-wizards.
A steam train which carried passengers in the 19th Century has returned to mark 150 years since the first tube journey.
A look back at some of the stops on London Underground's 150 year journey.
All day we've been adding fascinating facts about the Tube, which turns 150 years old this week. Now find out how much you know.