HUH????????? Is he really dead?!?!?

K im not a big Justin Beiber fan at all. I just think hes a little on(yeah i know its weird haha just somethin i will call a young boy if they are somewhat cute) and I was watchin SNL last night and he was on there! And so today i looked up a song on my youtube cause i kinda liked it and i thought it was a nice song. And im lookin threw all the comments on the video and they are like "RIP" or "he died so soon" and so im wondering...Is he really dead? cause thats horrible. and if so, what from? and how does everyone know for sure hes dead?