Prince Constantin was supposed to attend the international forum "together we are stronger" by the charitable foundation Football Is More that he is the president of. The third son of Prince Hans-Adam II was scheduled to give the opening speech for the event that dealt with the topic of "how the football, a truly world sport, using its charisma as a versatile platform for social engagement can create role models and serve as a role model" and featured a bunch of high profile speakers from the world of football (or soccer if you are American). I, however, can't seem to locate him on the official picture, so whether he was actually in attendance at the event held in Bad Ragaz, Switzerland isn't quite sure.
Meanwhile in Luxembourg, Grand Duke Henri and Grand Duchess Maria Teresa were also supposed to attend an event yesterday but likewise, there is no photographic evidence of them being actually present. The Société Générale Bank and Trust celebrated their 120th anniversary at the Centre Drosbach and according to the agenda of the cour the Grand Duke and Grand Duchess were supposed to attend an academic session and reception to mark the occasion. -- They did indeed.
Source: VSport, FIM, CGD