Who is Gossip Girl? For five years, that's been the secret she'll never tell.

This fall, however, the show's biggest mystery will finally be revealed!

In a new promo teasing the final season, which gets underway Monday night, executive producers Stephanie Savage and Sara Goodman promise that by the end of the 10-episode farewell, we will have our answer.

The cast members themselves are asked for their theories, which include:

• Dan
• Jenny
• Dorota
• Blake Lively's dog Penny
• Vogue editor Anna Wintour 

Pretty fun promo, and pretty cool that they're going to answer the question at all. Who do YOU think Gossip Girl is? Someone we know or a character we haven't seen before? Share your guesses below!

Steve Marsi is the Managing Editor of TV Fanatic. Follow him on Google+ or email him here.