Sneak Peek: Briana Reveals A Huge Family Secret In The Brand-New Teen Mom 2 Special

And the revelation will change the young mom's life forever

Some families have secrets -- and Teen Mom 2's Briana is about to reveal one about her own brood.

"I have a brother," Briana tells her sister Brittany in the clip above from the brand-new Teen Mom 2 special "Briana's Family Secret." "What the f*ck? I just don't understand."

Briana's limited information: Her sibling's name is Kevin, he is 14 years old and he lives in New York.

So how did Briana find out this lifechanging news, and what is Brittany's reaction? Watch the entire video, and do not miss Briana's special tonight at 8/7c.