I went searching on the web, since I can't just make a trip half way around the world right now.
I looked up Weesp and I went to the address that is stamped on the picture.
"Bertram Philip Sigismund Albrecht of HRR Empire Graaf Van Gronsveld Diepenbroick Impel (1715-1772) The portrait was painted by GJJ the Spinny in 1759" is listed HERE.
Sorry O.M., but this is a portrait of Bertram Philip Sigismund Albrecht - just as it states. Everything that I come across points to this.