She played a motherly role — on and off the set — in “The Godfather.”

Diane Keaton’s Hollywood breakthrough came in the Francis Ford Coppola 1972 masterpiece, where she starred as Kay Adams-Corleone, the schoolteacher wife of mobster Michael Corleone, played by Al Pacino.

Before that, Keaton, only 26, had acted in only two other films. Yet she nurtured a fledgling co-star.

“Diane was a good friend and very kind to me during the filming,” actor Gianni Russo recalled to The Post on Saturday. 3

Russo, 81, who played Carlo Rizzi, vicious husband to Michael’s sister Connie, played by Talia Shire, said Keaton was always there if he needed her.

“She couldn’t believe ‘The Godfather’ was my first movie. She said, ‘If you have any questions just ask me,’ and I did,” he recalled. 3

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