Al Pacino met mobster for Michael Corleone research

However, the 84-year-old writes in his memoir he was virtually clueless about how to play the character until he met a mafiosa at his home – where he ended up boozing and being shown a gun.

He reveals in his book Sonny Boy, he was struggling with how to play the character.

"I still had to figure out who Michael was to me," he said.

"Michael starts out from a young man we've seen before, getting by, a little loopy, a little lumpy. 

"He's there and not there at the same time. It's all building up to when he volunteers to take out Virgil Sollozzo and Captain McCluskey, the drug dealer and the crooked cop who conspired to kill Vito Corleone, Michael's father. All of a sudden, there's a big explosion in him."

"This is mapped out in the novel, because a book can give the narrative as much time as it needs. You wait and see how it unfolds. But what was I going to do in the film?"

Pacino finally got to grips with what to do after his Godfather co-star Alfredo Lettieri – who played heroin trafficker Virgil Sollozzo - took him him to a mobster's home.

"Little Al brought me to a traditional, beautiful, well-kept home. He took me inside and introduced me to the head of the household, a guy who looked like a normal businessman," he said. 

"I shook his hand and said hello, and he was very welcoming.

"He had a loving family. He had a wife who served us drinks and light snacks on fine porcelain.

"He had two young sons around my age. I was just some crazy actor who had come into his house, trying to absorb as much as I could. 

"I was being given a taste of how this thing looked and operated in reality, not how it was shown in the movies," he said. 

"Not that our host was going to get into any of those details with us. As a matter of fact, we ended up drinking and playing games. 

"Many moons later, photos from that night surfaced, showing me in a sweatshirt, laughing away with a drink in my hand, while Little Al showed me a gun. A boys' night out."