Kylie Jenner and half-brother Rob Kardashian are on less than good terms following news he's been romantically linked to Blac Chyna.
"Kylie is livid," a source tells PEOPLE.
"She feels super betrayed and can't understand why someone in her own family would stab her in the back like that."
Blac Chyna, whose birth name is Angela Renée White, is Tyga's ex-fiancée, and together they have a son, King Cairo, 3.
On Monday, Blac Chyna shared an Instagram photo of herself wrapped in the tattooed arms of Kardashian, seemingly announcing her new relationship with Jenner's sibling.