His 21-year-old daughter, Brittany, has given birth to a boy — Parker Brett. The little gunslinger weighs in at 7 pounds, 7 ounces.
Grandpa Brett says on his Web site that he and wife Deanna are "very proud" to welcome their first grandchild.
Favre has yet to announce whether he will return to the Vikings and play a 20th season in the NFL. Last year the 40-year-old enjoyed one of his best years and helped lead the Vikings to the NFC title game.
The baby's arrival was first reported by the Minneapolis Spokesman-Recorder.
The NFL says it knows of no other grandfathers among current players.