I think that your teacher meant "Speak of the devil" which is the short form of the idiom "Speak of the devil and he doth appear". It is used when an object of discussion unexpectedly becomes present during the conversation. For example, if Alice and Bob start discussing Charlie while he isn't in the room, and Charlie walks into the room, Alice or Bob might say, "Speak of the devil!"

/speak of the devil/ ... It is quite uncommon that the same idiom is shared among languages, but we say the same (translated) words in Italian, in precesily the same kind of contexts: / parlando del diavolo, spuntano le corna/, which is: speaking of the devil, the antlers appear.

ok, thanks Maryam! ; )

Exactly the meaning in English!! as jura said

and what does it mean Maryam?