Taylor Swift Cheat Song is BS ... Calvin Wrote It Pre-Tom

7/7/2016 8:37 AM PDT

Taylor Swift: That Cheat Song is BS ... Calvin Harris Wrote It Pre-Tom Hiddleston

EXCLUSIVE

Calvin Harris was working on his so-called cheating song long before Taylor Swift hooked up with Tom Hiddleston ... according to several sources.

According to the sources, Taylor knew all about "Olé" because Calvin started writing it before Tom was in the picture. One source told us, "If Calvin claims he wasn't working on this before the Met Ball, he's lying."

The Met Ball in early May is a key moment in the breakup. You'll recall Calvin did not go to the gala with Taylor ... and she was seen dancing the night away with Hiddleston that night. 

Here's the rub. In the song, Calvin wrote, "Low key you won't tell none of your friends about me." As you know, Tom famously play Loki in 'Thor.' Using the words "low key" would be a big coincidence.

Nevertheless, we're told Taylor's convinced Calvin is just trying to market his tune with a cheap trick.