Rihanna's pops found out about his soon-to-be grandkid same as everyone else -- while watchin' her Super Bowl halftime show ... and he's hoping, once again, for 2 X chromosomes.
Ronald Fenty tells TMZ ... he's over the moon about his daughter and A$AP Rocky's new kiddo, and with 4 grandsons already, he's hoping RiRi can shake things up with a girl.
He says he's excited at the prospect of having a granddaughter ... face it, he had great luck in that department with his famous daughter.
Ronald tells us Rihanna got him tickets to the big game, without telling him she's eating for 2 -- so he was insanely surprised when he spotted the bump from the stands ... telling his partner, "Oh my god! My baby girl looks pregnant!"
As we reported, Ronald was crossing his fingers for a girl this time last year when it was first revealed Rihanna was pregnant ... saying he had a feeling they wouldn't stop at just 1.
Ronald says he hasn't been involved with RiRi and A$AP's son's life yet ... referring to her super busy schedule and his living in Barbados.
Ronald and Rihanna have had a rocky relationship, but he says he'd love to be a part of her new baby's life.