"The Favourite" star had originally been credited on Swift's liner notes under the pseudonym William Bowery, helping to pen the tracks "Exile" and "Betty", which he also co-produced, alongside four other songs on the 2020 release.
"Folklore" claimed the top honor at music's big night last month (March 21), making Swift the first female artist in history to win the accolade three times.
She shared the prize with producers Aaron Dessner and Jack Antonoff, but now eagle-eyed fans have noticed Alwyn's name has also been added to the winners' list on the Grammys website, meaning he would have received his very own award, reports People.com.
The stars, who have been careful to keep much of their romance under wraps, have yet to comment on the news, but Swift gave her man a special shout-out during her acceptance speech at the prestigious event.
"Joe is the first person that I play every single song that I write, and I had the best time writing songs with you in quarantine," she smiled.
The couple has been dating since 2016.
Swift has also confirmed that Alwyn used the pseudonym William Bowery when talking to Dessner and Antonoff in Disney+ film, "Folklore: The Long Pond Studio Sessions". She first stated, "There's been a lot of discussion about William Bowery and his identity. He's not a real person."
The 31-year-old continued explaining, "William Bowery is Joe, as we know." She went on to gush, "And Joe, Joe plays piano beautifully, and he's always just playing and making things up and kind of creating things."