The "Love Story" singer took to Instagram on Wednesday, November 13 to share the news with fans, revealing pal Camila Cabello's boyfriend is an artist she has been "dying to collaborate with," adding she even gave Mendes permission to rewrite some of her lyrics, calling the venture a "COLLABORASHAWN."
"He's rewritten parts of it, which I think is so important because I love him as a writer, and I also think that everybody would write a different love letter to their lover," she says in a video clip. "And I think his take on it is so beautiful. I can't wait for you to hear it."
Mendes also took to the photo sharing site to express his excitement over the song, writing, "Thank you @taylorswift for letting me join you on such a beautiful song."
Taylor has actually dedicated her solo version of the track to her actor boyfriend Joe Alwyn.