After reading everybody's thoughts on what Brenda'a big secret could be, I started digging around transcripts from Franco's last arc in November. I found this:

Franco: Well, we always think the good things will last forever. We don't ever think they'll hold us down. They can go in a heartbeat.

Carly: Is that what happened to you?

Franco: Her name was Lauren. Best thing in my life.

Carly: Your wife?

Franco: No. My daughter. My wife was a bitch.


Some had mentioned that Brenda could be connected to Franco somehow and that maybe she was the wife he spoke of. I was thinking that if that were the case, maybe that's how Franco knew about Jason and why he began obsessing with him. Brenda could have mentioned him and Sonny to Franco?