"Taylor Swift wrote 'This Is What You Came for' under the pseudonym Nils Sjoberg," the pop star's rep told E! News Wednesday, confirming a fan rumor.
Music performing rights databases show "This Is What You Came for" was co-written by both "Nils Sjoberg" and Harris, who used his real name—Adam Wiles. E! News has also learned Swift came up with the melody.
"And she sings on a little bit of it too...Amazing lyric writer and she smashed it as usual. I wrote the music, produced the song, arranged it and cut the vocals though. And initially she wanted it kept secret, hence the pseudonym," Harris tweeted.
"Hurtful to me at this point that her and her team would go so far out of their way to try and make ME look bad at this stage though," he added.
After the single's release, Harris on Ryan Seacrest's radio show On-Air With Ryan Seacrest that he and Swift had never spoken about a music collaboration, adding, "I can't see it happening, though."
Swift was hurt by his words, E! News has learned.
"Adam and Swift did get in an argument about this but Adam was very hesitant in working with Swift on music because his past experience with his other girlfriend," a source told E! News exclusively, referring to Rita Ora. "He thinks Taylor is a talented artist but he wanted going forward to keep his relationship and work separate. He apologized if she took anything to heart but has only respected her throughout their relationship."
"This Is What You Came for" debuted on the Billboard Hot 100 Singles chart soon after its release and soon reached No. 4, marking the highest position Harris has ever reached on that chart.