The destination was unknown but an unlikely duo have been spotted together on the London bus.
But it was new parents William and Kate that were swamped by members of the public taking photographs as they walked along the high street to the station's entrance hall.
William, who left his post as an RAF search and rescue helicopter pilot in September, and Kate were greeted at the station by motorcyclists from the RBL's Riders Branch.
As they approached the station's entrance, they were introduced to a line-up of Poppy Day supporters including volunteers and military personnel.
Kate, wearing a red LK Bennett coat, spoke with Corporal Steve Johnson, who is busking at Tube stations across London to raise funds for the appeal.
"Kate asked what kind of music I'd been playing," he said. "She asked me to play but then said don't because it's too busy.
"Kate was more interested in the music, while William was more concerned with the day itself and how the appeal was going.
"Lots of people are ecstatic to see them."
The Duke and Duchess also chatted with retired volunteer Tim Connolly who has been selling poppies at the station after nearly 40 years raising funds for the appeal.
"They asked how the appeal was going and whether we were getting support from the public," he said.
"The answer is we're getting a lot of support. The public is responding when they see uniformed personnel out collecting for the appeal."
Another volunteer, said she had never seen the poppy design worn by the Duchess who appeared to have used three poppies to create one emblem.
"I must do it when I get home," she said.
Sisters Lisa and Sina Durchstecher, from Germany, were walking past the station when the royal couple emerged.
"It was a dream, we're so happy," Lisa, 24, said.
"I couldn't say anything when I saw them."
William and Kate had earlier boarded the bus at Kensington Palace with dozens of RBL supporters including actress Barbara Windsor and newsreader Alastair Stewart.
William told the former EastEnders star his son George had been "behaving himself this morning" as they met in the palace grounds.
Before boarding the bus, the Duchess told members of the RAF she had had flying lessons on a "fixed wing".