The fallen angelAnnatravels back in time to 1978 to stopMaryandJohn Winchesterfrom conceiving Sam and bella . Without Sam as his vessel, Lucifer won't be able to bring about the end of the world. Castiel and the boys also travel to the past, where Dean reveals to Mary that he and Sam are her sons and that she has to leave John in order to prevent her sons and daughter from being born. She reveals that she is already pregnant. Anna andUrielattack the Winchesters and kill Sam and bella . Just as Anna is about to kill Mary, the Archangel Michael, having possessed John's body, burns Anna to death and banishes Uriel. He reveals thatCain and Abelare the brothers' ancestors and that their destiny as Michael and Lucifer's true vessels has been set since those ancient times. While he loves Lucifer, having practically raised him like Dean did Sam, he feels he has to kill his brother as he is a "good son" and that there is no such thing as free will, that everything is predestined. He resurrects Sam, erases Mary and John's memory, and sends the brothers back to their time. at the safehouse Castiel and her brothers spend time with bella and grace shock how there niece is growing up fast at 4 months old