And if you remember that Fredo was under Don Francesco's protection, and that he was often informed on the well being of Fredo, it is not likely that Francesco called up anybody but Don Corleone to inform him about his son.
"Fredo, you're my older brother, and I love you. But never take sides against the family again. Ever."
-Micheal Corleone-(The Godfather)
| 
