After the defeat at Tinchebray, Robert was a prisoner of his brother, but he was still duke of Normandy. Henry I summoned all the magnates of Normandy to a council at Lisieux in the middle of October 1106. At Lisieux Henry firmly established peace throughout Normandy ‘by his royal authority’ and all robbery and plundering was to cease. Henry also announced that all churches were to hold their possessions as they had held them in 1087 and that all lawful heirs should hold their inheritances. The king took into his own hands all his father's demesnes and ‘by judgement of wise counsellors decreed that all the gifts his brother had foolishly made to ungrateful men, and all the concessions he had made through weakness, should be null and void’. By making 1087, specifically the day his father William the Conqueror had died, the reference point, Henry was, in effect, consigning Robert's rule in Normandy to oblivion. Henry's statement at Lisieux had the potential to set in train as many grievances over lands and other possessions as it was designed to settle. It resembles statements made by his father as he established his regime in the months after the battle of Hastings, when references to his predecessor as king, Edward the Confessor, effectively wrote King Harold II out of official memory.

Robert had a significant role to play in the surrender of the remaining ducal strongholds in Normandy to his brother. There is a sense in which Robert recognised the hopelessness of continuing the struggle, although concern for the well-being of his young son, William, may have made the duke apprehensive. Robert had fought to keep his duchy, but it was unlikely that he could withstand a determined campaign by his brother backed by the overwhelming financial resources of the kingdom of England.

Robert was sent into captivity in England at the end of 1106. There may have been protests because Henry made repeated attempts to justify his actions in subsequent years. Orderic hinted at the disquiet that Robert's defeat and capture caused when he described Robert de Bellême's attempt to secure the aid of Count Helias of Maine in order to continue the war against Henry. Robert de Bellême appealed to Helias saying that he needed his help: