"Kate asked what kind of music I'd been playing," Corporal Steve Johnson, an RAF recruitment officer from Newcastle, who is busking at Tube stations across London told the Press Association. "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."
More top news
An 11-year-old girl was sexually assaulted in broad daylight attack in a cemetery, police said.
The Mayor of London is one of several familiar faces popping up when the show returns to screens for its fifth series in November.
Here is a timeline of some of the key events in the debate over expansion of airport capacity.