Wallace Shawn, Leighton Meester, John Shea Wallace Shawn, Leighton Meester, John Shea

Blair Waldorf's big day has finally arrived! But who's she marrying... or not marrying? We won't spoil that surprise (and let's be honest, these days it could be anyone — Louis, Dan, Chuck...), but we can share a few fun tidbits from Gossip Girl's milestone 100th episode (Monday at 8/7c on The CW).

1. A dance sequence?
No, not like this. At the show's 100th episode party, Blake Lively gave us this perplexing scoop. In one scene, Serena wears a Marilyn Monroe get-up and sings "Diamonds Are a Girl's Best Friend" to suitors Nate, Chuck and Dan — that is, until someone else steals the show.

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2. A totally tubular serenade
We all know that Blair has a thing for '80s pop music (remember when Cyndi Lauper performed at her birthday?), so it's no surprise that her royal wedding soundtrack would include a cover of this Pat Benatar hit.

3. A Princess Bride reference!
It's amazing that it's taken the writers this long to have Princess Bride star Wallace "Inconceivable!" Shawn, who plays Blair's stepfather Cyrus, reference his iconic role. "We've been wanting to do it forever," executive producer Josh Safran says. Adds executive producer Stephanie Savage: "Gossip Girl said it, we've had episodes called that, we just finally had to put it in his mouth." As you wish!

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4. Blair's two dads
Who will walk her down the aisle? Her Paris-based biological dad Harold or sage stepdad Cyrus? Why should she have to choose?

5. Georgina's back!
And Girlfriend knows how to work a fascinator (and altar-boy vestments too apparently)! When Georgie-Girl (Michelle Trachtenberg) reappears, it's to sully Blair's marital bliss, but she also has one heck of an exit.

6. A game-changing reveal
Executive producer Josh Safran says the episode is a game-changer. "I know we've said that before, but unlike any other episode, it really will change the series forever," he says. "There's a revelation that is so big that it could only happen in the 100th episode." Hmm, what could it be? A game-changing reveal on a show called Gossip Girl?

What do you think the game-changing reveal is? Check back after the show for our postmortem of the episode!