20 celebrities you didn’t remember were on ‘Gossip Girl’

• “Gossip Girl” was a popular teen drama that ran for six seasons on The CW and featured appearances from several celebrities.
• Tyra Banks, Lady Gaga, and Kristen Bell (who also narrated the series) are some famous faces who guest-starred on the “Gossip Girl.”
• Visit INSIDER’s homepage for more stories.

“Gossip Girl” ran for six seasons on The CW and built up a loyal fanbase of viewers who tuned in to see the drama unfold on the Upper East Side. And now, a new reboot is in the works.

The original show also had some famous fans, who ended up guest-starring or making cameos.

Before he starred in “The Social Network” and “Call Me by Your Name,” Armie Hammer was a jerk who messed with Blake Lively’s Serena van der Woodsen, and “Jessica Jones'” star Krysten Ritter played Lilly’s sister in flashbacks. There were also some cameos from model Karlie Kloss and Lady Gaga, who played themselves.

Here’s a look back at some of the best celebrity surprises.

Lady Gaga performed her song "Bad Romance" as part of a performance art piece on the show's third season.

Watch the scene.

Read more: 45 photos that show how Lady Gaga's style has evolved through the years

Model Karlie Kloss plays herself attending a fashion party on the premiere of the fourth season.

Watch the scene.

Armie Hammer plays Gabriel, a jerk who pretends to date Serena van der Woodsen to get at her money.

Watch a scene.

Cyndi Lauper made a cameo as herself at Blair Waldorf's 18th birthday party on an episode of season two.

Watch the scene.

Hilary Duff played Olivia Burke, a movie star who had a brief fling with Dan Humphrey, during season three.

Watch a scene.

Read more: THEN AND NOW: What all of your favorite Disney Channel stars are up to

Tyra Banks played Ursula, an actress alongside Hilary Duff's Olivia, who becomes friends with Serena after she was hired as her assistant.

Watch a scene.

Krysten Ritter was Lily Rhodes' sister Carol during flashbacks on season two.

Watch a scene.

"Pitch Perfect" star Brittany Snow played the young Lilly in the same flashbacks.

Watch a scene.

No Doubt made a cameo during one of the flashbacks, performing at a club young Lilly goes to.

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Olympic gymnast Nastia Liukin made a brief cameo talking to Chuck Bass on season two.

Watch the clip.

"Harry Potter" actress Clémence Poésy played Chuck's girlfriend for a couple of episodes on season four.

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"Arrow's" Willa Holland played a young model who befriended Jenny Humphrey on a couple of episodes of season two.

Watch a scene.

"Arrow" star Katie Cassidy was also on the show, but during its fourth season. She started a relationship with Nate while going after Serena.

Watch a scene.

"Riverdale" fans know Mädchen Amick as Alice Cooper, but she was on the second season of "Gossip Girl" as Catherine, an older woman who had an affair with Nate Archibald.

Watch a scene.

For three seasons, "Avengers" star Sebastian Stan played Carter Baizen, a rival of Nate and Chuck who had a messed-up relationship with Serena at various points.

Watch a scene.

Read more: THEN AND NOW: The 'Avengers' stars before they were famous

Aaron Tveit played Nate's cousin Trip van der Bilt on seasons two, three, and five.

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Jared Kushner and Ivanka Trump played themselves hosting a New York Observer party, a paper which Kushner owned, on a season four episode. They greet Lily and Rufus Humphrey.

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Rachel Bilson played herself auditioning for a movie adaptation of Dan's book on the series finale.

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Kristen Bell, who voiced the narrator throughout the show's run, appeared in the same scene as herself. It was her first on-screen appearance on the show.

Watch the scene.

Read more: THEN AND NOW: The cast of 'Veronica Mars' 14 years later

Deadmau5 deejayed at Eleanor Waldorf's fashion show on the third season.

Watch the scene.