Instagram @anna.kepner16 / Inside Edition Composite

Anna Kepner 's ex has come forward with harrowing new details about the final moments of her life ... alleging she was involved in a heated confrontation with her 16-year-old stepbrother before her death.

Joshua Tew -- who described Anna as his first love during a new interview with Inside Edition -- said her 14-year-old brother Connor told him about a nasty fight she was allegedly in with her stepsibling in the cabin they all were sharing aboard Carnival's Horizon ship.

Anna and the unnamed brother were allegedly inside the locked cabin ... and according to Joshua, Connor could hear him "yelling at her in a harmful way." Joshua was told the stepsibling even yelled at her to "shut the hell up." There was also some "banging around"

See Full Page