User blog comment:Disney & Nick fan/Another Across the 2nd Dimension Promo!/@comment-5151799-20110529132105/@comment-5151799-20110529202207

That actually makes sense. Regular Doofenshmirtz and Alternate Doofenshmirtz, both being evil, could easily become best friends. And the "and it's me" part could allude to the fact that Alt. Doof IS actually Reg Doof. but in a parallel dimension. As well, "Doof Duet" might mean two Doofs, and "He's Doof" could be referring to either Regular or Alternate Doofenshmirtz.