If you recall, Furious 7 ends with Brian basically retiring from the game. The last we see of him, he's playing with Mia, his pregnant wife, and his son on a beach before one final friendly race with Dom. The Fate of the Furious ack**wledges that Brian is still out there living a peaceful life. In a scene when the gang realizes they're in trouble, Roman (Tyrese Gibson) utters that "Brian would k**w what to do." Letty shuts him down: "**, we can't bring Brian and Mia into this, we agreed."
There's a larger **d, but it's a big spoiler. If you're cool with that, read on.
The big twist in The Fate of the Furious is why Dom turns on his team. What could make him go against his family?! MORE FAMILY. The villai**us Cipher shows him that she's holding Elena (Elsa Pataky) hostage . . . with the baby Dom didn't k**w he fathered. Elena says she hasn't named him yet, because she thinks his father should name him. A bunch of other stuff happens next, but at the end of the movie, Dom finally introduces his baby to the crew - as Brian.
It's predicable from the moment Elena says she hasn't named the baby, but it's still kind of beautiful.