Complex sentence: When Robert I died in 1035 his illegitimate son His Grace Duke William inherited his father's title and several powerful Nobles, including Gilbert of Brionne, Osbern the Seneschal and Alan of Brittany, became His Grace Duke William's guardians.
Split into simpler sentences: When Robert I died in 1035 his illegitimate son William inherited his father's title. Several leading aristocrats, including Gilbert of Brionne, Osbern the Seneschal and Alan of Brittany, became William's guardians.