I understood that Sinatra was very against Godfather Part I as he felt it was a slur on the
Italian American Community.
He believed that the character of Johnny Fontane was based on him and was upset by this implication.
But after the great success of Part I, I believe he had a re-think and would have liked to be in Part II.

What can you say? - you gotta admire the man's inconsistency!!!!!