Matthew Vaughn recently did an interview where he addressed this rumor/theory that's been floating around for almost 3 years now -- namely, that T-Swift is the mysterious author who penned the manuscript for "Argylle" ... which is being made into a film of the same name.

The writer goes under the pseudonym of "Elly Conway" -- the same name of the main character in the flick -- and her real identity hasn't been revealed whatsoever. So, Swifties have been eating up perceived Easter eggs that they think point to Taylor (more on this in a bit).

Unfortunately for them, Vaughn's now saying it's all BS -- telling Rolling Stone ... "I'm not a big internet guy, and it was actually my daughter who came up to me -- this is the power of celebrity and the internet -- and said, 'You never told me Taylor wrote the book!'"

He adds, "And I’m looking at her going, ‘What are you talking about Taylor Swift wrote the book? She didn’t write the book!’ And I was laughing because I was like, ‘It’s not true! She didn’t write the book!’ But my daughter was convinced of it."

MV then says much more definitively ... "[T]here is an Elly Conway who wrote the book, but it’s not Taylor Swift. And I say that because I imagine Taylor Swift has a load of people trying to jump on her bandwagon left, right, and center. I don’t want to be a part of that club. I did read the conspiracies and I was like, ‘Wow, they don’t leave a stone unturned!’ But it’s not Taylor Swift. She definitely didn’t write the book."

Part of the reason Taylor's legion thought she might've been the author is because of all these subtle things they thought referred to her -- including the Scottish Fold cat featured (she has 2 herself), the fact she wears argyle sweaters, and other "hints" fans picked up on.