This happened with Erica's eldest daughter, Kendall Hart-Slater, not once, but twice! First with her half-brother Trey Kenyon whom she felt an instant connection and attraction to but didn't know why, and who came to town specifically looking for his family, fell in lust with her and almost slept with her before it was revealed that she was his sister.
Her mother stepped in Just in Time to prevent them from going any farther, and dropped the bomb that they were half-siblings through one of Erica's father's many liaisons. Narrowly avoided when Erica Kane was engaged to Mark.
