Prince Harry broached the subject of Brexit with a dairy farmer while on walkabout with his family at The Mall.
However, the Royal kept his own views close to his chest when chatting with Mike King, 46.
He and his wife Rachel, 48, had gone to the event from their home at Iron Acton, near Bristol.
Mr King said: “I told Harry we were farmers and were hardy so we’re just used to the wet. When he heard we were farmers he said ‘in or out?’ and I said I was going to ask him the same. I said: ‘I’m undecided’, and he said: ‘I’m not allowed to say’.”
Harry was in a light-hearted mood and he joked about the Queen’s bright neon green outfit she wore for Saturday’s Trooping the Colour ceremony.
Ann Gimson from Kent, who celebrated her 90th birthday yesterday, said: “He was talking about outfits and asked what we thought about the Queen’s dress.
“He said: ‘Neon at 90, should we encourage more?’ and then he told us she would be wearing pink today.”
The prince made fun of the umbrella ban and said to Andrew Easton, 34, “You’re not allowed to this”, as he waved an umbrella at him.
Kate, who wore a dress by Roksanda, was kissed on the hand by Spanish-born Nielson Sanchez-Stewart, 70, who lives in Marbella and travelled over especially for the event.
He said: “I kissed her hand, this is what we do in Spain when a lady arrives. It’s very romantic.”