Complex sentence: It was not until September 24 that he spoke concerning the document to his fellow workers and to his chief, Colonel Sandherr, who immediately informed the head of staff, General de Boisdeffre, and the secretary of war, General Auguste Mercier.
Split into simpler sentences: It was not until September 24 that he spoke about the document to his fellow workers and to his chief, Colonel Sandherr. Sandherr immediately informed the head of staff, General de Boisdeffre, and the secretary of war, General Auguste Mercier.