AceShowbiz -

Justin Bieber discusses the challenges that come with being popular in a new sneak peek at his upcoming docu film "Believe 3D". In what seems to be a reference to his ex-girlfriend Selena Gomez, the teen singer talks about masking his emotion and smiling through his pains.

"I could be going through a big argument and I'm like, 'I'm about to go onstage right now.' And we're yelling, and then I gotta rise up on the toaster," he says. "It's like, I'm upset. I don't want to have to smile and put on a happy [face], but sometimes you just gotta suck it up."

"That's just one of the things you gotta deal with being in this position, in this world, in this industry," the teen adds. He also states, "You always gotta keep a smile on your face through all the negativity. You gotta hide your emotions sometimes, especially for me going onstage."

The 3D movie will be released in the U.S. on Christmas Day this year. Following up the successful 2011 documentary "Justin Bieber: Never Say Never" directed by John M. Chu, it will focus on the singer's transition from teen pop star to young adult during the making of his album "Believe" and the tour that followed.