Taylor Swift owned the song she secretly helped write for Calvin Harris ... not only lip syncing it, but posting it on social media.
Taylor was at the Tommy Hilfiger fashion show in NYC Friday when the DJ blasted "This Is What You Came For."
You'll recall ... after Taylor and Calvin broke up, she laid claim to the song, but Calvin fired back it was almost all him.
She was in the credits under the pseudonym Nils Sjoberg as the songwriter/composer, but later changed it back to her own name.
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