Camilla, the Duchess of Cornwall, joked she was "self-isolating" as she stepped into an air raid shelter at the London Transport Museum.
She and the Prince of Wales were on a visit to the museum, where they were marking Transport for London's 20th anniversary, when she entered the display.
She stepped briefly into an old air raid shelter which was on display.
Then, in an apparent reference to coronavirus, she quipped: “I’m self-isolating.”
The duchess wore gloves during the engagement but Charles did not. The couple shook hands with some of those they met.
Charles and Camilla had enjoyed a ride to the museum on an electric bus.
They boarded the red double decker at a specially installed temporary bus stop outside Clarence House.
As they sat at the front they took in views of central London which were somewhat obscured by the rain.
The environmentally friendly bus, accompanied by a police escort, took the couple, TfL staff and a group of schoolchildren on the 10-minute journey down Pall Mall.
They went past Trafalgar Square to Covent Garden.
During a tour of the museum, the couple sat in a 1938 Tube carriage and recorded a message.
This will be played on the capital’s transport network at some stage later in the year.
They also met TfL apprentices and staff who have pioneered environmental and mental health schemes in the workplace.
In addition they saw as crisis response staff, as they walked around the building with Mayor of London Sadiq Khan.
