The she-wolf and the lion

Chapter 47 - "how did Lyra know?"

"And how did Lyra know about any of this? Until now when she's married to Jaime?" The septa asks.
"Jaime of course told her about Cersei and her tricks, long ago, before they were actually betrothed", Tywin says. "Jaime and Lyra have no secrets from each other and they never have."
"And how did lady Lyra react to it?" The septa asks.
"I would lie if I told you she was happy about it, she was honestly furious", Tywin says. "She didn't feel safe around Cersei or having her sons around their aunt."
"Why didn't she feel safe around her or didn't feel safe having her sons around her?" the septa asks.
"Because Cersei has tried to bed Jaime multiple times, and because she tried to kill lady Lyra with a planted knife in her and Jaime's bed when she found out that Lyra was pregnant with my eldest grandson", Tywin says. "Lyra felt the knife against her back when Jaime laid her down on their bed, the knife was planted there by a handmaiden at the Rock."
"What happened to the handmaiden after she did that?" the septa asks.
"She was sent away to the silent sisters", Tywin says. "After request from me and lord Benjen, lady Lyra's father, we found it to be a good enough punishment for trying to assassinate our children and our at the time unborn grandson."
"For trying to assassinate your son's wife and the mother of his children and your grandchildren, I think that punishment is wise, m'lord", the septa says. "Although I don't think the seven would have blamed you or lord Benjen or anyone of your houses if you had that handmaiden killed for what she did and tried to do to your son and his wife."
"And had they not noticed the knife in their bed, it would have looked like Jaime stabbed his lady wife in the back and killed her while he was on top of her", Tywin says. "And Cersei would indirectly very likely have killed her brother, cause Jaime would very likely have been sentenced to death for murder, had I not been able to stop the king from ordering the death of my son."
"And Cersei would have had to live the rest of her life knowing that she killed her brother", the septa says.
"Yes, had they not found the knife lodged in the bed and it stabbed Lyra to death while she and Jaime were making love, Jaime would very likely have been blamed for her death and very likely would have been sentenced to death for murder and Cersei would have had to live the rest of her life with the blood of her brother, her brother's wife and their unborn child, on her hands", Tywin says.