Belieb

After Alice Wu angrily insisted that she was talking to Justin Bieber via video call (in fact the Wire taking Bieber's form), the Tenth Doctor humourously said "Don't you belieb it" in response. (PROSE: Loose Wire)

Behind the scenes
A "belieber" is a term used to describe fans of singer Justin Bieber, being a clear play on his second name and the word "believer".