The royal couple then met some of the soldiers and their families for lunch in the welfare centre of the barracks where the longest-serving Guardsman in the battalion proposed a toast to and thanked the Duchess for presenting the shamrocks.
The black-tie event, hosted by Mr Llewellyn, will celebrate the friendship and cultural ties between the United Kingdom and France, and among the guests will be celebrities from the worlds of film and sport.
In a nod to the famous Parisian fashion house, Kate wore a Chanel striped cotton tweed waisted frock coat with a box pleated skirt.
But after witnessing Prince William and Princess Kate in Paris, body language expert Dr. Lillian Glass said that they showed “no sign of a problem”.
Later today the royal couple will meet French Second World War veterans at the historic Les Invalides site and a number of victims and members of the emergency services From the Bataclan and Nice attacks.
Kate wore a tweed Chanel dress and black pumps, while William looked dapper in a navy suit, a white button-down shirt and a maroon tie.
In addition, Prince William and his friends also reportedly spent time with 24-year-old Australian model Sophie Taylor and a 30-year-old British former beautician named Rosie Peate. On Friday, William and his wife, Kate Middleton, head to Paris for an official two-day trip.
The couple also plans to attend a France-Wales rugby match.
For Prince William, it’s also a chance to put this week’s media backlash behind him after being seen partying in the Alps on a “boys only” ski trip featuring cringeworthy “dad dancing”.
On an interview a year ago, he said he was aware of the criticism and willing to take on more royal duties.
The Foreign Office said the royal visit, the first of its kind carried out by William since the death of his mother Princess Diana in the city in 1997, would be used to “promote closer ties” with France.