Complex sentence: His uncle, Ludovico Sforza, acted as regent to the young duke but quickly wrested all power from him and became the de facto ruler of Milan, and later the duke after Gian Galeazzo's death, widely viewed as suspicious.
Split into simpler sentences: His uncle, Ludovico Sforza, acted as regent to the young duke but quickly wrested all power from him and became the de facto ruler of Milan. Ludovico later became the duke after Gian Galeazzo's death, which was widely viewed as suspicious.