Imagine hearing a knock on your door, and suddenly Justin Bieber is standing right in front of you. On FOX’s Knock Knock: Live one lucky fan was given a super-sweet surprise by the Biebz—a quinceañera! Ahead of tonight's episode the "Where Are Ü Now" singer graciously tweeted "No better feeling than giving back" and we couldn't agree more.
Can't decide between the Weeknd or Paul McCartney, Florence + the Machine or Bassnectar, Sam Smith or Metallica? Answer these 10 questions and figure it all out