Clarence House has tweeted pictures of Prince Charles using an Oyster card to pass through the ticket gates at Farringdon Station.
The Prince of Wales and the Duchess of Cornwall are visiting the station to mark the 150th birthday of the tube.
The royal couple were presented with special commemorative Oyster cards.
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.