Gossip Girl Spoilers: Chuck. Blair. Sex. 

According to E! Online, relations, "of the bom-chicka-bow-wow kind," will take place between Chuck and Blair in season 4, which begins September 13.As for the return of the Upper East Siders in general, Penn Badgley sums it up best...
parole chiavi: season 4, chair, Blair Waldorf, chuck basso