Grey's Anatomy first premiered on March 27, 2005, and has remained a powerhouse medical drama ever since.
Fans immediately fell in love with the OG surgical interns, including Meredith, Cristina, Izzie, Alex, and George, as well as authority figures like Dr. Miranda Bailey and Dr. Richard Webber. And, of course, we can't forget about Meredith's heartthrob affair partner-turned-husband, Dr. Derek Shepherd, also known as "McDreamy."
The show followed the original cast as they all delved deeper into their careers, encountering riveting medical cases and plenty of interpersonal relationship drama along the way.
However, since Grey's Anatomy has continued running for 21 seasons, the show has needed plenty of extra, outside actors to portray patients, bereaved loved ones, and sometimes, other doctors. That's precisely how so many celebrities ended up making appearances on the beloved drama.
Let's take a walk down memory lane and revisit some Grey's Anatomy celeb cameos you might've forgotten even happened. Warning: spoilers abound.
Scroll to see all the Grey's Anatomy celebrity cameo you totally forgot happened!
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Fans of Grey's Anatomy know that one of the overarching themes of the show is Meredith's familial trauma and how it follows her into her adult life.
She was raised by Dr. Ellis Grey, a trailblazing female surgeon who struggled to balance her medical career with being a supportive mother. Meredith also has an alcoholic father, later learns about her mother's affair with Dr. Richard Webber, and winds up having two half-sisters.
So, in Season 6 Episode 15, actress Sarah Paulson, most known for her role in American Horror Story, starred as a young Ellis Grey in a flashback as she worked alongside Dr. Webber on a 1982 AIDs case.
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You might've forgotten how, in Season 2, Dr. Webber's 14-year-old niece, Camille, arrived at the hospital on her prom night. This important role was played by Tessa Thompson, who has been in movies like Thor: Ragnarok and Men in Black: International, as well as the popular TV show Westworld.
In this Grey's Anatomy episode, Camille gets busy with her boyfriend Brian when she passes out. It was discovered that Camille had ovarian cancer, so her surgical team removed one of her ovaries. Then, in Season 4, Camille returns after realizing her cancer has spread and she's going to die.
This was a gut-wrenching subplot that hit especially close to home among viewers due to the sheer love the fanbase developed for Dr. Webber.
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Sarah Chalke moved women everywhere with her performance as Kate Mularkey in the TV series Firefly Lane. However, years earlier, she also appeared on Grey's Anatomy as a terrified yet diligent single mother named Casey Hedges.
In Season 9, Episode 19, Casey arrives at the hospital with her young son, who is experiencing a host of symptoms that resemble a virus. Nonetheless, she doesn't back down and keeps researching until she ultimately helps her son get diagnosed with Kawasaki disease.
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Before Millie Bobby Brown became known as the powerful Eleven on Stranger Things, she joined the Grey's Anatomy cast for Season 11, Episode 15. She played Ruby, a little girl who called the hospital directly after her mother fell, and she wasn't able to get in touch with emergency services due to an earthquake.
Dr. Owen Hunt and Dr. Amelia Shepherd are forced to teach Ruby how to check her mother's breathing and perform chest compressions over the phone. Then, when the battery on Ruby's phone runs out, she's left on her own until emergency services show up.
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In Season 3, Episode 3, the young Abigail Breslin made a notable appearance as a patient of Dr. Alex Karev's. She starred as Megan Clover, a little girl who thought she had superpowers because she didn't have the ability to feel pain.
Megan was ultimately diagnosed with a rare genetic disorder known as congenital insensitivity to pain with anhidrosis (CIPA).
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Before Dylan Minnette took on his most famous role as Clay Jensen in 13 Reasons Why, he depicted an adorable little boy named Ryan in Season 4, Episode 5 of Grey's Anatomy.
Ryan was born with no external ears, so he goes "trick or treating for ears" with Meredith in order to get other surgical staff members on board for a pro bono ear reconstruction surgery.
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Ernie Hudson, the beloved Ghostbusters star, also made an unexpected cameo in Season 8, Episode 7. He played Dr. Brad McDougall, a doctor from Seattle Presbyterian.
Dr. Owen Hunt, who was, at that point, in the show, the Chief of Surgery, is trying to get his staff ready for a big softball game against the rival hospital. Ernie Hudson winds up delivering some nice trash talk as he leads his team on the diamond.
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Finally, you might best know Leslie Grossman from American Horror Story: Cult, but she played a woman named Lauren Hammer in Season 5, Episode 9 of Grey's Anatomy.
Lauren shows up at the hospital with stomach pain and believes she has cancer, but her husband, Seth, claims she's just a hypochondriac. In the end, it turned out she'd just given herself a staph infection from taking antibiotics she had purchased online.
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