Robert Griffin III -- My Baby Has Arrived, But Won't Be RG4

Robert Griffin III officially became a father Thursday, but he's going to have to wait a while for RG4 ... because his wife gave birth to a girl.

Rebecca Griffin squeezed out 7 lbs, 9 oz. of baby today ... and they named her Reese Anne.

Griffin posted a photo of the happy family, along with the Bible passage, "'For I know the plans I have for you,' says the Lord. 'They are plans for good and not for disaster, to give you a future and a hope.'"

Hope RG3 got a really, really good night's sleep last night. As he himself told us ... it's gonna be hard to come by now.