Speak of the Devil

“Speak of the Devil” simply means when a person mentioned in the current conversation happens to walk into the room.

Example of use: “We were huddled around the tv, talking about Fred, when he walked in. Well, speak of the devil!”

Interesting fact

During the 19th century, this pharse used to be a warning against eavesdroppers "No good of himself does a listener hear, / Speak of the devil he's sure to appear."