Complex sentence: In 1290 Siegfried renounced the government over his states and become in a preacher monk (German: "Predigermönch"); for this his eldest son Albert became in the new ruler of Zerbst, but the former Prince retain his rank until his death.
Split into simpler sentences: In 1290 Siegfried renounced his rule to become a preaching monk (German: "Predigermönch"). As a result, his eldest son Albert became the new ruler of Zerbst, although the former prince retained his rank until his death.