Complex sentence: In Munich in 1894 he embarked upon an affair with Franziska, Gräfin (ie Countess) zu Reventlow (Fanny zu Reventlow), who was pregnant with his child when in 1895 she married the politician Walter Lübke.
Split into simpler sentences: In Munich in 1894 he embarked upon an affair with Franziska, Gräfin (ie Countess) zu Reventlow (Fanny zu Reventlow). She was pregnant with Herstein's child when in 1895 she married the politician Walter Lübke.