Guillaume was the son of Geoffroy II but his mother is unknown. The date and place of his birth have not been found.
Guillaume de Donzy
Geoffroy II
Hervé I de Semur (c1005-1055)
Geoffroy II de Semur-en-Brionnais (c0955-1020)
Mahaut de Chalon (c0956-<1019)
NN de Vergy
NN de Châtel-Censoir