your pen is extremely likely to be fake. It is silly to sell a real montblanc in a fake package consciously. Even if the seller is in good faith, they may be making a mistake. My reasoning is, if the person that sold you the pen didn't recognize the fake package, he/she will certainly not recognize a fake pen.
More often than not, if the packaging is fake, the pen has a high probability of being fake as well. Photos will help, and even if it looks real in the photos, no guarantee can be given.
