Complex sentence: Castelnau met General De Langle de Cary the commander of GAC on 25 February, who doubted that the east bank could be held but Castelnau called Herr and ordered that the right (east) bank of the Meuse to be held at all costs.
Split into simpler sentences: Castelnau met General De Langle de Cary, the commander of GAC, on 25 February, who doubted that the east bank could be held. Nevertheless, Castelnau called Herr and ordered that the right (east) bank of the Meuse be held at all costs.