The long-running mystery identity of the narrator is solved! Up until now he's been referred to as the "Latin Lover Narrator," and there was a compelling theory that he could be Alba's late husband and Jane's grandfather, the OG Mateo, looking down on everyone. But now we know his true identity: a grown-up Mateo!
During the wedding ceremony, Mateo, Anna, and Elsa get up to give a sweet reading about love. When it's Mateo's turn, he takes one look at his paternal grandmother (aka Rogelio's mom aka Queen Rita Moreno) and screams out, "LOVE LETS YOU BE WHO YOU WANT TO BE!" As everyone laughs, he turns to Jane and says, "I practiced with Great Glam-ma; she said I'd be great at voice-over work."
That's when a dashing, different male voice from the heavens says, "And for the record, I am," then transitions back into the narrator's usual cadence to say, "But I'm getting ahead of myself." So, there you have it! Mateo grows up to be a voice-over actor and narrator. When you consider that Jane's book will likely be turned into a show within the show, it makes total sense that Mateo might be the one to serve as its narrator.