Brooke definitely likes to keep it all in the family, as evidenced by the fact that she married three different Forrester men at different points in her life. Of course, these were Eric (John McCook) and his sons, Ridge and Thorne (Winsor Harmon). However, marrying a father and his sons is not even remotely the worst of Brooke’s sins. According to Soap Hub, she also slept with Bill Spencer (Don Diamont) when he was married to her sister, Katie (Heather Tom), who was going through postpartum depression at the time.
Granted, Katie pushed them together when she wasn’t in her right mind, but she didn’t expect her sister to sleep with her husband (via Soaps In Depth). When she recovered and learned what happened, Katie divorced Bill, and Brooke eventually married him. However, that marriage didn’t last, and, like she did with her daughters, Brooke managed to salvage her relationship with her sisters, too.