Al Pacino, 83, Surprised By 29-Year-Old Girlfriend's Pregnancy

Al Pacino wasn't looking to become a new daddy at the ripe old age of 83 ... we've learned his girlfriend's pregnancy came as a total surprise to the actor.

Sources close to Pacino and 29-year-old Noor Alfallah tell us ... he was not gunning to have baby #4 in their fairly-new relationship. They've only been dating for a year.

Although it seems like a "no duh," there are a bunch of seniors who are intentional about producing offspring, like 73-year-old Richard Gere, who has a 2 1/2-year-old, a 4-year-old and a 9-year-old. And famously, there's Tony Randall, who was 77 when he and his 26-year-old wife had the first of 2 kids. Larry King was 65 when he had his son Chance, followed by son Cannon the next year. And, Billy Joel was 71 when he had his last kid.

TMZ broke the story ... Alfallah is 8 months pregnant, something she's been able to keep a secret, despite being spotted out with Al several times in the last month.

We don't yet know the sex of the baby ... but it'll be Al's 4th kid.

Al's got twins with actress Beverly D'Angelo -- 22-year-old Olivia and Anton -- and 33-year-old Julia with Jan Tarrant.

Baby Pacino will mark Noor's first. As we reported, she's dated other seasoned celebs, including Mick Jagger and billionaire Nicolas Berggruen, but no kiddin' with them.