E. Cobham Brewer 18101897. Dictionary of Phrase and Fable. 1898.
Bottes.
A propose de bottes. By the by, thus: Mais, Mons., à propos de bottes, comment se porte madame votre mère?
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That venerable personage [the Chaldæan Charon] not only gives Izdubar instructions how to regain his health, but tells him, somewhat a propos des bottes the long story of his perfidious adventure.Nineteenth Century, June, 1891, p. 911.