Your enemies will be all the more formidable because they have hitherto been your friends. Conduct that one expects from an enemy is atrocious in a friend.
 Honoré de Balzac, Lost Illusions (1843). copy citation

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Author Honoré de Balzac
Source Lost Illusions
Topic enemies
Date 1843
Language English
Reference
Note Translated by Ellen Marriage
Weblink https://www.gutenberg.org/cache/epub/13159/pg13159.html

Context

“You are a very clever journalist, but you will never make a politician. le Duc de Navarreins, his First Gentleman of the Bedchamber. The Minister denounced you to the King, and the King was so angry that he scolded M. Your enemies will be all the more formidable because they have hitherto been your friends. Conduct that one expects from an enemy is atrocious in a friend. "Why, really, my dear fellow, are you a child?" said des Lupeaulx. "You have compromised me. Mme. d'Espard, Mme. de Bargeton, and Mme. de Montcornet, who were responsible for you, must be furious. The Duke is sure to have handed on his annoyance to the Marquise, and the Marquise will have scolded her cousin.” source