After Michael returns, he becomes the new Don, with Vito retiring, and shortly thereafter, dying. Michael promotes Aldo to Caporegime. Learning the FBI are conducting an investigation into the Corleones, Michael sends Aldo and Monk to find out what they know. When Aldo arrives at the hotel used by the FBI, Monk tells him Michael has learned a Corleone informant is meeting with the FBI at that moment, and they are to kill him. They storm the hotel, and Monk kills a lone FBI agent, before escaping. Aldo realizes that Monk himself is the informant. Michael calls, telling Aldo he knew there was an informant but was unsure if it was Monk or Aldo, and the job was a ruse to smoke out the culprit. Aldo follows Monk, who admits he blamed the Corleone family for Frankie's death, and allied with the Cuneo family. Incredulous with Monk's betrayal, Aldo kills him.