William III Chatelain de St. Omer

William III Chatelain de was born about 1120 in St. Omer, France.  William III Chatelain de's father was William II Chatelain de St. Omer and his mother was Melisende de Picquigny. He had a sister named Mahaut de.  He was the younger of the two children.  He died in 1170.