So, the obvious question is ... who in Taylor's inner circle is rocking the mic behind the mask?!?
There's a ton of possibilities, and some huge names, because Taylor has been out with a bunch of famous hunks over the years ... like Harry Styles, Jake Gyllenhaal, Taylor Lautner, John Mayer, Joe Jonas and Zac Efron ... just to name a few.
But, it may not be an ex. One source with direct knowledge tells TMZ ... the person behind the mask also collaborated with Taylor on a project.