Oskar is the second son of Wilhelm-Karl Prince of Prussia and of his wife Armgard von Veltheim.

They have three children: In 1995 Oskar was awarded a Ph.D. in history by the Free University of Berlin for his dissertation about the relationship between the Emperor Wilhelm II and the United States.

[2] Since 1999 Oskar has been Herrenmeister (Grand Master) of the Order of Saint John (Bailiwick of Brandenburg).

[4] In 2013 Oskar represented the Bailiwick at an ecumenical celebration in Berlin to observe the 900th anniversary of the Knights Hospitaller.

[5] On June 25, 2021, he welcomed the President of Germany, Frank-Walter Steinmeier, to the Johanniter Hospital in Treuenbrietzen.