Hey Upper East Siders, Gossip Girl here, and Serena van der Woodsen is getting a little nostalgic. On Sept. 21, Blake Lively celebrated the 18th anniversary of her breakout series Gossip Girl by posting never-before-seen throwback photos with many of her former co-stars, including her ex-boyfriend Penn Badgley and the late Michelle Trachtenberg. “The summer gossip girl turned 18...,” Lively captioned the post. Blake’s Gossip Girl ReunionLively has been feeling a surge of Gossip Girl nostalgia lately. Lively shared the reunion on Instagram while nodding to a Gossip Girl meme by captioning the post, “Go.