Their father had decided that the older son, Richard III, would succeed him as duke. Robert would became Count of Hiémois. In August 1026 their father, Richard II, died and Richard III became the fifth duke. But once Richard III began to reign, Robert was not satisfied with his position. He raided the diocese of his uncle Robert II, Archbishop of Rouen. He also captured his brother's city of Falaise. Robert's rebellion lasted through the end of 1026 and into early 1027. Finally Richard III laid to Falaise and brought the walls down. Robert surrendered and promised his .