King Charles and Queen Camilla are travelling from Washington DC to New York to visit the 9/11 memorial ahead of the 25th anniversary of the 11 September attacks, as part of their historic state visit to the US.
The royals will meet first responders and families of those killed that day, and lay flowers at a memorial pool.
Earlier, Buckingham Palace responded after president Donald Trump claimed that King Charles agreed with him that Iran should not be allowed to obtain a nuclear weapon.
Members of the royal family never express political views, and are constitutionally required to remain strictly neutral on politics.
But at a formal state dinner on Tuesday night, President Trump said the US would never allow that opponent to obtain a nuclear weapon – and surprised guests by suggesting the King shared that view.
“Charles agrees with me even more than I do,” Trump said, before reiterating that Iran would not be allowed to develop nuclear arms. In his own comments later, the King did not speak about Iran or the Iran war.
A Palace spokesperson responded: “The King is naturally mindful of his government’s long-standing and well-known position on the prevention of nuclear proliferation.”