It's OK, he didn't bring Chris Brown with him, that would've been off the scales for innumerable reasons. In this instance, Bieber just so happened to be recording in the vicinity of Chatsworth, which is just North West of Hollywood (for those of you interested in geography), so he decided to pop the head into the local prom which was merrily underway. 
Then this happened (overlook all spelling mistakes; it's twitter and they were very excited - it's amazing they maintained any control over their digits)
 

Then (presumably) the prom queen got involved...

Since you ask - No. No Justin turned up to my 'prom' (on account of him being an infant at the time), and given the reaction of those present, myself and my fellow Debs attendees will be forever thankful for that. We didn't need any more variables to have us falling over, thanking you. Now, if Blur and/or Oasis had turned up, that would've been a different matter entirely. 

Via Uproxx