PREVIEW: Cassie finds out devastating news about Lucas; Shawn forces the truth out of Philip. SUMMARY: Rex and Mimi rush to the hotel where they find Lucas and Cassie in bed together. Rex is horrified and disgusted to think that Cassie has slept with their half-brother, and struggles to get Cassie on her own. Once an exasperated Lucas finally leaves, Rex tells Cassie that she just slept with their half-brother! Cassie is shocked to learn that Kate Roberts is their mother, but admits to Rex that she and Lucas didn't sleep together. Rex swears Cassie to secrecy, and she tears out of the hotel room. Back at the apartment, Sami is furious that Lucas stood her up, and doesn't believe his explanations that Will didn't tell him about the dinner. Lucas tells her that it's none of her business who he dates, and suddenly, Cassie is at the door. Sami is initially furious to see Lucas's new 'girlfriend' at her home, until Cassie tells Lucas that his touch makes her sick and she never wants to