India, Oct. 13 -- Al Pacino is said to be filled with regret for not marrying Diane Keaton after years of an on and off romance that began in the 1970s. Keaton, who died Saturday in California at 79, played Pacino's on-screen partner in "The Godfather" trilogy, and their real-life relationship began in 1974. The two split in 1990 after Keaton reportedly gave him an ultimatum about marriage that he turned down.

Pacino, now 85, wishes he had married her, a source told the Daily Mail.

"I know he will forever regret he didn't make his move when he had the chance," a friend of the actor said. "For years after he and Diane split, Al used to say, 'If it's meant to be, it's never too late for a do-over.' But sadly, now it is."

"Looking back, A...