LBJ's Mistress Blows Whistle On JFK Assassination!!! The night before the Kennedy assassination, Lyndon Baines Johnson met with Dallas tycoons, FBI moguls and organized crime kingpins - emerging from the conference to tell his mistress Madeleine Duncan Brown that "those SOB's" would never embarrass him again. It's a jaw-dropping deposition and it's the biggest JFK smoking gun there is - despite the fact that it has received little media attention.