Lady Gaga
It wouldn't be a true party if the Upper East Siders didn't have at least one A-list musician performing for all to see. In the season three episode "Last Days of the Disco Stick," the pop star appeared on stage to perform "Bad Romance."
Karlie Kloss
In the season four premiere, the model attended one of Lily Van Der Woodsen's posh parties.
Rachel Bilson & Kristen Bell
In the series finale, Rachel and Kristen prepared to audition for the role of Serena and Blair in Dan's upcoming movie when Dan revealed he's the one behind Gossip Girl's account.
Gwen Stefani
The No Doubt singer performed in a seedy club during one of Lily Van Der Woodsen's flashbacks on season two.
Hilary Duff
The Lizzie McGuire Show actress starred as movie star Olivia Burke in season three of the series. She and Dan become an unlikely couple, but things went sour when they had a threesome with Vanessa, who Dan realized he's in love with. Olivia then announced she's been cast in a new movie and leaves for good.
Armie Hammer
The Call Me By Your Name actor played conman Gabriel in season two of Gossip Girl, in which he quickly married Serena, cheated on her and then stole the money Rufus had put aside for Dan's college tuition.
Sebastian Stan
The Marvel star portrayed bad boy Carter Baizen for 11 episodes, before Serena literally kicked him to the curb in season two's "The Unblairable Lightness of Being."
Melissa Fumero
Before she was chasing bad guys in Brooklyn Nine-Nine, the actress had a brief stint as one of Blair's headband girls in seasons three and four.
Rachel Zoe
Blair and the rest of the Waldorfs were totally embarrassed when the designer was knocked into a chocolate fountain. This is made all the more humiliating because Elle's Creative Director Joe Zee and Cynthia Rowley, along with musician Robyn, were there to witness it all go down.
Robyn
Speaking of Robyn, the Swedish singer mortified Blair by bringing a video of the Upper East Sider singing off-key at a karaoke bar. It's unclear what vendetta the pop star had against Blair.
Alexa Chung
The model and fashion designer starred as herself in the season six episode titled "Dirty Rotten Scandals."
Mike Bloomberg
In the season finale, the former New York City mayor was shocked to learn Gossip Girl was not Dorota, as he originally suspected.
Krysten Ritter
Remember when The CW almost made a spinoff show about Lily Van Der Wooden's life in the '80s? Gossip Girl gave viewers a look at the potential series when they had Krysten portray Lily's big sister, Carol Rhodes, in the season two episode titled Valley Girls.
Tyra Banks
The model had a guest role as Ursula Nyquist in season three of The CW series.
Florence Welch
The Florence + The Machine lead singer set the tone to a rather sad episode with her acoustic rendition of "Cosmic Love."
Tinsley Mortimer
The Real Housewives of New York City alum made a cameo in season two of the series.
Madchen Amick
In season two, the Riverdale actress portrayed Duchess Catherine Beaton, who was introduced as Nate Archibald's lover. She was also the stepmom of Serena's boyfriend Marcus, who she also ends up having an affair with.
Cyndi Lauper
For Blair's 18th birthday, her mother's boyfriend, Cyrus, hired Cyndi Lauper as the ultimate gift, thus earning the affections of the birthday girl herself in the season two episode "Bonfire of the Vanity."
Willa Holland
For seasons two and three, The O.C. actress ditched her west coast roots when she took on the role of Agnes Andrews, who is arguably one of the more evil characters and Jenny Humphries frenemy.
Elizabeth Hurley
As per usual, Nate Archibald found himself falling for an older woman when Elizabeth's character Diana Payne emerged in the New York social scene. And, as always, things went awry when Gossip Girl got involved.
Nastia Liukin
The Olympic gymnast made a pass at Chuck, who was nearly tempted to slink away with her into the shadows. That is, until Blair walked up and shooed the athlete away in typical Blair fashion.