Grey’s Anatomy is a medical drama that began airing in 2005 and has become a really popular show over the years. The series began with a group of medical interns who just started at a fictional hospital in Seattle and has followed their lives in and out of the hospital. The series follows the patients that come into the hospital and the way that the doctors have to deal with trying to cure what ails them as well as what’s going on in their personal lives.

The main cast of the series has expanded and changed over the years and on top of that, there have been a ton of guest stars that have appeared on the series for only a short period of time. Visiting doctors, patients, and family members show up for an episode or a short storyline before leaving and, often, we kind of forget about them because there are just so many.

To see 10 celebrities you totally forgot had guest appearances on Grey’s Anatomy, keep reading!

Millie Bobby Brown

Millie Bobby Brown is still a teenager, but she’s also one of the biggest stars in Hollywood right now. She really broke onto the scene as one of the main characters in Stranger Things and will be starring in the upcoming 2020 film Enola Holmes.

But, before she was the huge star that stole all our hearts as Eleven in Netflix’s science fiction series, she actually had a guest appearance on Grey’s Anatomy. She appeared in an episode of the 11th season of the series and played a girl named Ruby whose mother was injured during a camping trip, forcing her to care for her over the phone following directions from the Grey Sloan Memorial staff.

Sarah Paulson

Sarah Paulson is an actress who has become known for a variety of different shows and movies. Most notably, she’s appeared in American Horror Story, but one role that not so many people remember is the one she played in Grey’s Anatomy.

Even though she only appeared in a single episode during the sixth season, she was still a pretty major character. Paulson appeared in a flashback in that episode and played a younger version of Meredith’s mother, Ellis Grey. She’s normally portrayed by Kate Burton and the two of them definitely have a believable resemblance!

Demi Lovato

Demi Lovato may be a famous pop star now, but her most dedicated fans will remember that she got her big break in Hollywood as an actress on the Disney Channel. But, Camp Rock and Sonny With a Chance are far from her only acting credits.

Lovato also appeared in an episode of Grey’s Anatomy in the sixth season. She played the role of Hayley, a psych patient whose parents brought her to Seattle Grace Mercy West Hospital, leading to a major struggle between her, her parents, and the doctors as they try to carefully diagnose and treat her symptoms.

John Cho

John Cho is an actor who is best known to his fans for appearing in movies like Searching and the Harold & Kumar films, but he’s also had roles in a variety of TV shows over the years, too.

For this guest star, we’re going to have to think way back to the second season of the series. That feels so long ago, right? It was before that 007 scene broke our hearts and before Cristina was left at the altar. They were simpler times, that’s for sure. In one season two episode, John Cho appeared as Marshall Stone, a surgical intern who felt the physical and mental toll that interning takes on a person when he fell asleep driving and caused a major accident.

Christina Ricci

Christina Ricci is an actress that has been in a variety of movies and TV shows over the years. She really got her big break in Hollywood back in the 1990s in movies like The Addams Family, but Grey’s Anatomy fans probably remember her better for playing the role of Hannah Davies on this medical drama during the second season.

Although she was only in a couple episodes, she still played a big part in a very serious storyline. In the series, she played Hannah Davies, a paramedic who used her hand to stop a wound’s bleeding, only to find out that her finger was the only thing stopping the bomb inside of her patient from detonating.

Mandy Moore

Since her career started, Mandy Moore has gone from being a pop star to being an actress. These days, she’s best known for being on the tearjerker This Is Us. But, before she was on that dramatic show, we saw her in another equally intense TV series.

She was a recurring character on Grey’s Anatomy in the sixth and seventh seasons of the series. Moore played the role of Mary Portman and many fans will likely remember that Mary and Dr. Bailey were trapped in Mary’s recovery room together when Gary Clark brought a gun into the hospital.

Keke Palmer

Keke Palmer is an actress and singer that initially rose to fame on the Nickelodeon series True Jackson VP. Since then, she’s gone on to be in a variety of other movies and TV shows as well as releasing music. But, many fans may forget that she also appeared on Grey’s Anatomy for a short time.

During the 10th season of the series, Cristina was running a trial for HLHS and Keke Palmer played the role of Sheryll, a young woman with a heart condition that wanted to be part of Cristina’s trial after she became pregnant and became concerned for her health and future.

Tessa Thompson

Tessa Thompson is an actress that has become known for playing the role of Valkyrie in the MCU as well as appearing in music videos for Janelle Monáe’s music. Although she’s become a huge star now, many people may still forget that she had a small role in Grey’s Anatomy.

She played the role of Camille Travis, niece of Richard Webber, during the second season of the series. Many people may forget that Tessa Thompson played the role of Camille because of the fact that the actress that played her changed during season four!

Dylan Minnette

Dylan Minnette is an actor that had a few roles before he landed the lead in Netflix’s 13 Reasons Why, including movies like Don’t Breathe, but Netflix’s dramatic novel adaptation is definitely the role that he has become best known for since 2017.

Long before he was playing the role of Clay Jensen, he had a guest spot on Grey’s Anatomy. Although he was a lot younger then, he’s still totally recognizable and hard to miss once you notice that it’s him! He appeared in an episode of the fourth season as one of Mark Sloan’s patients who is looking to get reconstructive surgery on his ears.

Holland Roden

Holland Roden is best known for playing Lydia on Teen Wolf and Zoe on Channel Zero. But if you’re a serious fan of this actress or of Grey’s Anatomy, you might remember that she also had an appearance on this medical drama, too!

During the eighth season of the series, Roden played the role of Gretchen, the mother of a pair of conjoined twins who had been in Arizona’s care since their birth. During the episode, Gretchen has brought her children into the hospital in order to have surgery to have the two of them separated by a team of doctors at the hospital.

Next: 10 Best Medical Dramas (Aside From Grey’s Anatomy), Ranked