Complex sentence: When Count Palatinate William of Birkenfeld-Gellnahusen, who became later the first Duke in Bavaria, resided in the palace from 1780 onwards the facade of the German building was altered in French Neo-classical style and the so-called "Birkenfeld Rooms" were constructed.
Split into simpler sentences: When Count Palatinate William of Birkenfeld-Gellnahusen, the later first Duke in Bavaria, resided in the palace from 1780 onwards. The facade of the German building was altered in French Neo-classical style and the "Birkenfeld Rooms" were constructed.