François III of Kergroadez is regarded as the single building owner of the rebuilding of the castle. On August 4, 1598, it accepted royal letters setting up its ground of Kergroadez in marquisat, at the same time as it was seen giving the collar about Saint Michel in reward of its rallying in 1595 to the royal party (with the detriment of that of the Mercoeur member of a league) to the sides of the governor of Brest Rene de Rieux, lord de Sourdéac.

It is enough trying to make coincide these two events with the launching of the construction of the new castle of Kergroadez. The pacified context left with this lord the leisure devote to the illustration of its House all while equipping it with an apparatus defensive at the same time emblematic and conditioned by the close memory of the disorders of the League. The date of 1598 could be well that of the launching of the building site of Kergroadez.