Il est venu fort à propos = He came very opportunely.

À propos, viendrez-vous ce soir? = By the way, shall you come this evening?

L'à-propos fait le mérite = Seasonableness gives everything its price.

À propos de bottes = With reference to nothing in particular; With no reference to the subject in hand.

Il le dit à tout propos = He says it on every occasion, at every turn.

Il l'a fait de propos délibéré = He did it of set purpose; He had made up his mind to do it.

Il l'a fait fort mal à propos = He did it very unseasonably, just at the wrong time.