When Nivelle was dismissed and replaced with Philippe Pétain, Castelnau was recalled to the command of the Eastern Army Group where he commanded the advance into Lorraine in 1918.
== Življenjepis ==Med leti 1912 in 1914 je bil načelnik štaba maršala Joffreja; pomagal je izdelati strateški Načrt XVII za ponovno zavzetje Alzacije in Lorene.