Prince William
Prince William returns from Mustique vacation and attended Pictured: Prince William attends the unveiling of The Victoria Cross Commemorative Paving Stones representing each of Birmingham's 1st World War recipients at the Hall of Memory, Centenary Square on Dec. 7, 2015 in Birmingham, England. Getty Images/Richard Stonehouse

Prince William and Kate Middleton have returned from their Mustique vacation and the duke just made his first engagement after their holiday.

On Wednesday, the Duke of Cambridge stepped out to attend the commemorations marking the centenary of the Battle of Amiens in France. Prince William greeted British Prime Minister Theresa May, who gave him a curtsy, and gave the opening reading at Amiens Cathedral.

"I am delighted to join you all today to mark this important centenary in this historic cathedral of Amien," Prince William said about being part of the event (via People). "From the very first start of the First World War, Amien found itself at the heart of the conflict. For most of the war, it was just behind the allied front lines and military personnel soon become a familiar sight around its streets, around its shops, cafes and hotels."

"For thousands of servicemen it became a home away from home, above all Ambien was a city of connections – its railway line was a vital link between Paris and the north. Here the armies of France and the British Empire came together – it connected the allies. During the defence of the city against the great German offensive in April 1918, shelling and bombing destroyed many of the buildings here. Thankfully, this great cathedral was spared significant damage," he continued.

Middleton's husband was also seen laying flowers in the Chapel of Allies. There were about 2,000 guests who attended the ceremony which featured readings from diary extracts, letters, poems and personal accounts from those who were present.

The said sighting was Prince William’s first public outing following the reports that they were in Mustique. Last week, the Duke and Duchess of Cambridge were seen attending a night out party in the private island. They were also photographed dancing.

Prince William and Middleton were expected to attend Charlie van Straubenzee and Daisy Jenk's wedding on Saturday. They were supposed to join Prince Harry and Meghan Markle at the event. However, the couple didn't make it in the ceremony based on the photos. Although, there were speculations that they attended the reception.

It's also possible that the couple was still in Mustique at that time. Prince William and Middleton flew to the Carribean island with their three children and Middleton's parents, Carole and Michael over a week ago.