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25 'Grey's Anatomy' Celebrity Guest Stars You Totally Forgot About

There's no doubt the set of ABC's Grey's Anatomy is basically an incubator for acting talent. Actors such as Ellen Pompeo, Katherine Heigl, and Sandra Oh became household names thanks to their roles on the hit medical drama. But it's not just the regular cast, who fans will instantly be able to recognize; there have also been a ton of Grey's Anatomy celebrity guest stars who bring even more star power to the small screen, and they show up in episodes pretty often.

Grey's seems to be one of the stops many actors take on their way to stardom in the entertainment industry. Many of the talent listed below got their role on the medical drama before they hit "big time" fame in other roles later in their careers. For already established actors, a Grey's cameo also seems a bit like a bucket list item, as there also many celebs who've appeared on Grey's after they're already well-known for other roles.

In 16 seasons of Grey's, there are plenty of episodes out there that feature celebrity guests — some of which fans may have missed the first time watching the series. So, take another look at these episodes to revisit your fave guest-star moment, and rediscover some surprise cameos.

1. Elisabeth Moss

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The lead of Hulu's The Handmaid's Tale once starred in Season 3, Episode 19 as Nina Rogerson, a concerned daughter of a patient needing high-risk surgery.

2. Millie Bobby Brown

Before Stranger Things, Millie Bobby Brown starred in Season 11, Episode 15 of Grey's Anatomy. She played Ruby, a girl who saved her mother's life after an earthquake.

3. Mandy Moore

Moore played Mary Portman, a recurring character in Seasons 6 and 7 of Grey's. Her character was in the hospital for a surgery when it was shut down due to an active shooter. She came back to the hospital six months later for the surgery, but ended up in a coma and eventually died.

4. Demi Lovato

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Lovato played Hayley May in Season 6, Episode 22 of Grey's. She was first misdiagnosed with schizophrenia, but Alex Karev saved the day when he discovered she had Superior Canal Dehiscence Syndrome and treated her via surgery.

5. Sarah Paulson

Before American Horror Story and American Crime Story, Paulson played a young Ellis Grey (Meredith's mother) in Season 6, Episode 15.

6. Keke Palmer

Palmer played Sheryll Jeffries in Season 10, Episode 16 of Grey's. Her character came to the hospital pregnant, wanting take part in Cristina's trial for her hypoplastic left heart syndrome. However, Cristina denied her and she gave birth prematurely.

7. Christina Ricci

Ricci starred in the two-part finale of Grey's Season 2, in which she played a paramedic involved in a potential bomb situation.

8. Tessa Thompson

Thompson played Richard Webber's niece, Camille Travis, in Season 2, Episodes 26 and 27. She came to the hospital after passing out on prom night and found out her ovarian cancer had returned. Since Grey's, Thompson has starred in many projects, including Westworld, Men in Black: International, and Avengers.

9. Abigail Breslin

Breslin starred in Season 3, Episode 3, as a young girl who couldn't feel pain.

10. Katie Lowes

Lowes played a blood donor in Season 7, Episode 22 of Grey's. Fans may also know her for her role as Quinn Perkins in ABC's Scandal. Shonda Rhimes is the creator behind both shows, so it makes sense she'd use the same actors in some of her projects.

11. Scott Foley

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Foley played Henry Burton in 15 episodes throughout Seasons 7 and 8 of Grey's. He first came into the hospital as an uninsured patient, but marries Teddy to get on her insurance and get his care. But just as soon as they were developing a real romance, Henry died because of a tumor. Foley has also had a long running role as Jake Ballard on Scandal.

12. Bellamy Young

Young is another Scandal actor who made an appearance on Grey's. She played Kathy in Season 3, Episodes 22 and 23 — Private Practice crossover episodes. Her character sought help with sex in her relationship.

13. Jeff Perry

Notice a trend yet? Perry played Cyrus Beene in Scandal. He also played Meredith's father, Thatcher Grey, until his character died in Season 7.

14. Dylan Minnette

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Before 13 Reasons Why, Minnette played Ryan, a boy needed constructive ear surgery, in Season 4, Episode 5 of Grey's.

15. William Daniels

Daniels may be well known for his role as Mr. Feeney on Boy Meets World, but on Grey's, he played Dr. Craig Thomas. His character was a cardiothoracic surgeon at the Mayo Clinic and a mentor of Cristina Yang's. He starred in five episodes throughout Seasons 8 and 9 of the medical drama.

16. James Avery

Avery Starred in Season 8, Episode 17 of Grey's Anatomy. He played Sam, a man who had to unplug his husband from life support. If Avery looks familiar, it's probably because he played the role of Uncle Phil in The Fresh Prince of Bel-Air.

17. Matthew Morrison

Morrison played Paul Stadler on Grey's, a well-known surgeon, but also the estranged, abusive husband of Jo. He starred in four episodes throughout Seasons 13 and 14 of the medical series. Morrison is also well-known for his role as Will Schuester on Glee.

18. Jamie Chung

Chung played Trina Paiz in Season 7, Episode 10 of Grey's. Her character came into the hospital after falling over 100 feet into a ravine and suffering an ear injury.

19. Constance Zimmer

Zimmer has credits on major shows like Entourage, House of Cards, Shameless, and UnReal, so it's no surprise her acting chops landed her a spot on Grey's. On the medical show, she starred in five episodes in Season 8, as Alana Cahill, a physician advisor who helped Seattle Grace Mercy West Hospital avoid bankruptcy after it had to shell out $75 million to the doctors who were victims of the plane crash.

20. Rachel Brosnahan

Brosnahan may now be best known for her role as Midge Maisel in Amazon Prime Video's The Marvelous Mrs. Maisel, but before that role, she was in Season 9, Episode 14 of Grey's.

21. Wilmer Valderrama

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Valderrama famously played Fez in That '70s Show. On Grey's, he played Kyle Diaz, a musician with multiple sclerosis. His character died after five episodes in Season 12.

22. Alyssa Milano

Milano played Haylee Peterson in Season 16, Episode 3 of Grey's. Her character was the sister of someone who had fallen into a construction site and became brain-dead as a result.

23. Elizabeth Reaser

Twilight fans' favorite undead mom, Esme Cullen, was played by Reaser from 2009 to 2013. Before that role, though, she played Rebecca Pope in Seasons 3 and 4 of Grey's. Her character suffered brain damage and memory loss after a ferry accident, and bonded with Alex Karev while in the hospital. Eventually, she recovered her memories and tried to pursue a real relationship with him, but things did not work out.

24. Jurnee Smollett-Bell

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Birds of Prey actor Smollett-Bell played Beth Monroe, a patient with a tumor that left her partially paralyzed. Her character appeared in Episodes 16 and 17 of Season 4.

25. Hector Elizondo

Fans may recognize Elizondo for his role as Joe the driver in The Princess Diaries movies, but he also played Carlos Torres, Callie Torres' dad, in five episodes (over Seasons 3, 5, 6, 7 and 10).