LONDON, April 8, 2024 (BSS?AFP) - French and British troops on Monday swapped roles to take part in changing of the guard ceremonies outside the palaces of the other country's head of state, in an unprecedented move to celebrate 120 years since the Entente Cordiale.

Signed in 1904, the Entente Cordiale accord cemented an improvement in relations after the Napoleonic Wars and is seen as the foundation of the two NATO members' alliance to this day.

Even after Brexit and with war back in Europe, "this entente cordiale is somehow the cornerstone... that allows us to maintain the bilateral relationship", French President Emmanuel Macron said in a video address on X, formerly Twitter.

"Long live the entente cordiale and long live the Franco-British friendship," he said, switching to English.

Macron and British ambassador to France Menna Rawlings on Monday morning watched British guards taking part in the changing of the guard outside his Elysee Palace.

French guards then did the same in London outside Buckingham Palace, the official residence of King Charles III. 

At the Elysee, 16 members of the Number 7 Company Coldstream Guards of the UK embassy, wearing their traditional bearskin hats, relieved French counterparts from the first infantry regiment.

The French army choir then sang the two national anthems -- God Save the King and La Marseillaise.

- 'More to defeat Russia' -

British Foreign Minister David Cameron and his French counterpart, Stephane Sejourne, celebrated their countries' "close friendship" in a joint op-ed published late on Sunday.

They said it was key at a time when NATO is mobilised to ensure Ukraine does not lose its fight to repel the Russian invasion.

"Britain and France, two founding members and Europe's nuclear powers, have a responsibility in driving the alliance to deal with the challenges before it," the diplomats wrote in Britain's The Telegraph newspaper.

"We must do even more to ensure we defeat Russia. The world is watching -- and will judge us if we fail."

A French presidential official said it was "the first time in the history of the Elysee" that foreign troops had been invited to participate in the military ritual.

At the end of 2023, Macron made the changing of the Republican Guard public again, on the first Tuesday of each month, although the ceremony is much less spectacular than its counterpart outside Buckingham Palace.

Two sections of the 1st and 2nd Infantry Regiment of France's Republican Guard participated in the London ceremony alongside guards from F Company Scots Guards and other British forces, the French presidential official said.

It was watched by the Duke and Duchess of Edinburgh -- Prince Edward and his wife Sophie -- accompanied by the UK chief of the general staff, General Patrick Sanders, and French chief of the army staff Pierre Schill.

The event on the forecourt of Buckingham Palace was the first time a country from outside the Commonwealth -- which mostly includes English-speaking former British colonies and possessions -- has taken part in the changing of the guard.

- Tensions after Brexit -

The signing of the Entente Cordiale on April 8, 1904, is widely seen as preparing the way for France and Britain joining forces against Germany in World War I.

While the accord is often used as shorthand to describe the Franco-British relationship, ties have been bedevilled by tensions in recent years, particularly since the United Kingdom left the European Union.

Migration has been a particular sticking point, with London pressuring Paris to halt the flow of migrants across the Channel.

But a state visit by King Charles last autumn -- one of his last big foreign engagements before his cancer diagnosis -- was widely seen as a resounding success that showed the fundamental strength of the relationship.