I believe that AD Michael (of the Hungarian branch) is a friend of the princess. He is the godfather of her son Pieter Christiaan while his wife Christiane of Lowenstein-Wertheim-Rosenberg is godmother of Prince Floris.
The man in the grey suit next to Princess Margriet doesn't resemble the Archduke though. So perhaps it is Archduke Michael of Austria-Tuscany (youngest brother of the Margravine of Baden), a descendant of Sisi through ADss Marie Valerie. I have never seen a picture of him but it is the only other Michael I could find.
They have been selling out the national museum/palace as they need to attract more visitors due to budget cuts. This museum recently had an exhibition about Grace of Monaco and now this. Both having nothing to do with Palace Het Loo, the Dutch RF or The Netherlands. I suppose Pss. Diana will be next... after that maybe they can do Cleopatra.