Spring 1940: So ... who was "Foch's Pupil"?

My grandfather wrote in his Journal 1940 about what he saw on May 11, 1940 (the day after the Nazis began their invasion of western Europe). 

A few things of note: 

1. I preserved his British spelling and occasionally incorrect verb tenses. (He wrote this journal to practice his English, which he was still learning. I'm still in awe of how clear and well-written it was, for someone who was writing in a foreign language).
2. I corrected his capitalization
3. I used American-style quotation marks.
4. I used hyperlinks to provide extra info for what are probably unfamiliar terms for most Americans.

     In the first important street near the maternity I saw a big crowd. Something happened on the pavement. A noise of many cars, motor-cycles and trucks could be heard. Setting myself on tiptoe I understood at once the matter. The British motorised infantry hurried to the front. The soldiers weared an uniform unknown to me. A very plate helmet on the top, short trousers and a shirt with large pockets in the front. They were all very young and merry. 

Gurkha Shorts

     The crowd was happy to see them coming so speedy to the rescue of Belgium. Men shrieked (shouted!), waving their hats. Women and girls send kisses and throwed flowers. The Englishmen replied showing the thumbs of their right hands directed down, which meaned, I suppose: "We shall show the Germans what we are!" The Crowd was obviously optimistic. In the Rue de la Loi where were the ministries I noticed three high French officers. I remember quite well the oldest of them. He had gray hair, big, lively eyes, seemed thoughtful but quiet. A man of the street trusted him. He was perhaps Foch’s pupil, or another great chiefs, winners of Verdun or Chemin des Dames, makers of the victory of 1918.

So, does anyone know who [Ferdinand] "Foch's pupil" was?  Was there anyone in particular who that might have been? A friend pointed out that my grandfather probably didn't know who the man was, and was speculating, and he may be right. But that doesn't mean there wasn't someone who was known by that or perhaps "L'élève de Foch."