Translation of 'apropos of nothing'

Question

What might be the translation of apropos, as commonly used in American English, that Spanish speakers would use in identical situations, the context being germane (to), in a broad sense?

Continuing that thought in context, is there an expression in Spanish that means the same as "apropos of nothing"?

Answer 1

The translation of "apropos of nothing" will vary according to context, for example:

• She kept smiling apropos of nothing. (Source) (Continuaba/continuó sonriendo sin motivo).

• Suddenly, apropos of nothing, he said, `You're such an optimist.' (Source) (De repente, de la nada, dijo: Eres todo un optimista.)

• Apropos of nothing, what do you think about her? ((No tiene) Nada que ver, pero ¿qué piensas de ella?)

Answer 2

The most used equivalent for "apropos" would be "Hablando de..." (Speaking of...).

Apropos of cars, I bought one! -> Hablando de coches, ¡me he comprado uno!

About "apropos of nothing", it would depend on context, as @Gustavson already told. My suggestions:

• Por nada en especial (for no special reason)
• Sólo por curiosidad (just for curiosity)
• Sin venir a cuento (literally, without coming in the tale): Me pegó una hostia sin venir a cuento <- She hit me in the face apropos of nothing.