Anna Kepner's stepbrother -- who was mysteriously found dead on a Carnival Cruise --allegedly had a strange infatuation with the teen cheerleader ... even climbing on her in bed one time, according to a new report.

"Inside Edition" interviewed Steven Westin -- the father of Kepner's ex-boyfriend -- for an episode that aired Thursday ... and Westin made several shocking claims based on discussions he says he had with his 18-year-old son about Kepner's stepbrother. Play video content

As you know, Kepner, also 18, was on the Carnival Cruise with her stepbrother and other family members returning to Miami on November 7 … when she was tragically found dead on board.

According to Westin, Kepner's stepbrother was totally obsessed with her and wouldn't stop pursuing her. Westin also claims Kep

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