The Duke and Duchess of Edinburgh’s three-day tour of Portugal began in classic fashion yesterday as the couple took their seats on one of Lisbon’s iconic yellow trams. After an almost 10-minute ride through the city, the Duke showed off his linguistic skills, thanking the driver with a quick “obrigado” as he and the Duchess arrived at their stop.

The pair kicked off their whistlestop tour earlier in the day at the Portuguese National Archive to unveil the first display of the original English and Portuguese copies of the Treaty of Windsor, together side by side for the first time since 1386. “The Portuguese are better at looking after their documents!”, the Duke said with a hearty laugh, noting the stains that have appeared on the English version of the treaty over the last 640 years.

Adding with a flourish that it “is always important to read the fine print”, Edward also took a special moment to thank the people of Portugal for their help in restoring Windsor Castle after the devastating 1992 fire.

Addressing guests, which included organisers and some of Portugal’s most noted historians, the Duke said: “I am also delighted that, in more recent times, after the tragedy of the fire at Windsor Castle, Portugal wanted to be involved in the restoration.

“We’re always very grateful for that offer. When you go into the Crimson Drawing Room, all the tassel work was completely done by the Portuguese, so you are very much at the heart of Windsor Castle.”

Dating back to 1386, the Treaty of Windsor remains the world’s oldest continuous diplomatic alliance, uniting England and Portugal. This historic military and political agreement was signed by King Richard II of England and King João I of Portugal after their shared victory against Castile at the Battle of Aljubarrota.

It was signed to establish a lasting bond of "perpetual friendship, union, and alliance," which was further cemented by the marriage of King João I to Philippa of Lancaster, Richard II’s first cousin through his uncle, John of Gaunt.

In addition to guaranteed military support, the treaty provided commercial benefits, enabling merchants to travel and trade freely across both countries.

And, despite being signed in the 1380s, this alliance has been successfully used during the Napoleonic Wars, World War I, and World War II.

Edward and Sophie's visit is an especially poignant trip as it is the first royal visit to Portugal since March 2011, when King Charles and Queen Camilla (then the Prince of Wales and the Duchess of Cornwall) last visited.