The Duke and Duchess of Edinburgh stepped in for the King as they celebrated Anglo-French relations at a ceremony marking the 120th anniversary of the Entente Cordiale.
Prince Edward, 60, and Sophie, 59, inspected UK and French troops on Buckingham Palace's forecourt during the parade highlighting ties between the two nations.
During the ceremony, the royal couple walked past 32 members of the 1st and 2nd Infantry regiments of the Garde Republicaine and then 40 guardsmen from F Company Scots Guards, lined up opposite their French counterparts.
See the moment in the clip below…
The King, who is continuing his cancer treatment, was not at Buckingham Palace as his brother and sister-in-law represented him at the outing.
Edward and Sophie, who were last seen publicly with the King on Easter Sunday, were joined by General Sir Patrick Sanders, UK Chief of General Staff, the French Chief of the Army Staff General Pierre Schill and France’s ambassador to the UK Helene Duchene.
It marked the first time a non-Commonwealth country has taken part in the Changing Of The Guard ceremony – although the French troops did not guard the royal residence.
Major Jamie Drummond-Moray, Officer Commanding F Company Scots Guards, said: "It is an enormous privilege for us to host the French here in London and to play such a significant part in a ceremony that has never happened before with a non-Commonwealth country.
"It really is a monumental occasion and more so given that it is marking 120 years of the strong relationship between the UK with France. I think it's a great honour for all our soldiers, and a fantastic day for everyone in France and the UK."
Sophie looked beautiful in a white midi dress with a cream trench coat and nude heels for the ceremony, and wore her hair styled up in a low bun, accessorised with floral-shaped earrings.
The Duke and Duchess of Edinburgh are parents to Lady Louise Windsor, 20, and James, Earl of Wessex, 16. While James accompanied his parents on Easter Sunday, Lady Louise was notably absent from the church service, thought to be due to her university commitments.
Edward and Sophie are among the senior royals to step in for the King as he continues treatment, alongside Queen Camilla and the Princess Royal.