He is visited by Don Michael Corleone on the advice of the elderly Sicilian Mafia boss Don Tommasino (Michael's Sicilian ally and his father's before him).
Michael receives a visit from Don Michael Corleone, who was advised to do so by the old Sicilian Mafia boss, Don Tommasino. This is because Don Tommasino is Michael's Sicilian ally and his father's predecessor.