© Photo: Getty ImagesAre you a fan of Grey's Anatomy? Having been on screens for nearly two decades, the show has seen plenty of cast members come and go over the years, including Sandra Oh, Katherine Heigl and Patrick Dempsey.
MORE: Grey's Anatomy boss shares regret over major character exit
But as well as the main cast, many other recognisable faces have popped up in the show over the years - some before they were even famous! For all the celebrity cameos you might have forgotten about, click through the gallery to take a look...
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© Photo: Getty ImagesDemi Lovato
Demi Lovato appeared in Grey's Anatomy not long after rising to superstardom in Disney's Camp Rock. A then 18-year-old Demi played a young patient misdiagnosed with paranoid schizophrenia who was going to be admitted into a psychiatric ward before the doctors realised she actually had a rare inner ear condition that was causing her to act erratically.
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© Photo: Getty ImagesMillie Bobby Brown
The year before her breakout role as Eleven on Stranger Things, Millie Bobby Brown appeared in season 11 of Grey's Anatomy as a young girl named Ruby who ends up saving her mother's life. In the episode, her character ingeniously calls the hospital after her mom is knocked out during an earthquake, with the docs at Sloan Grey talking her through how to do CPR over the phone until a helicopter arrives and rescues them both.
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© Photo: Getty ImagesElisabeth Moss
The Mad Men and The Handmaid's Tale alum appeared on the show all the way back in season three as the overly-protective daughter of a patient who suffered from a rare and disturbing bone disorder.
© Photo: Getty ImagesWilmer Valderrama
Wilmer Valderrama is best known to TV audiences for playing Special Agent Torres on NCIS, but before he landed the role, he had a five-episode arc on Grey's! He starred as a flirtatious musician named Kyle Diaz, who sought brain surgery to help alleviate his multiple sclerosis. However, things didn't go well, and he died, leaving Jerrika Hinton's Stephanie Edwards heartbroken.
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© Photo: Getty ImagesAbigail Breslin
Former child actress Abigail Breslin appeared in a season three episode as a little girl who is admitted to ER after her parents realise she is immune to pain.
© Photo: Getty ImagesMandy Moore
Mandy Moore was already an established star when she dropped by Grey's Sloan for one of its most dramatic episodes to date. She played a young patient who finds herself trapped inside the hospital during a shooting. She reprised her role the following season when she returned for a surgical procedure. Sadly, though, her character died after slipping into a coma during surgery.
© Photo: Getty ImagesKeke Palmer
During season ten, Keke Palmer checked herself in Grey Sloan. She played a young pregnant woman who ran away from home after being diagnosed with a rare, under-researched heart condition.
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© Photo: Getty ImagesChristina Ricci
Christina Ricci made a small but memorable cameo as a panicked paramedic who is forced to keep her hand on a wound inside a patient's chest to stop a bomb from exploding.
© Photo: Getty ImagesLeslie Odom Jr.
Hamilton star Leslie Odom Jr. appeared in a season five episode in which he played a young man who begrudgingly agrees to donate a kidney to his father - for a price! His character only decides to go through with the procedure after being offered $10,000 by his dad.
© Photo: Getty ImagesSarah Paulson
American Horror Story star Sarah Paulson appeared in a season six flashback episode as a younger version of Meredith's mother, Ellis Grey. Given that older Ellis Grey actress Katie Burton is back this season, we wonder if Sarah will also return?
© Photo: Getty ImagesTessa Thompson
Marvel star Tessa Thompson guest-starred in season two as Richard Webber's niece, who is rushed to hospital after passing out during prom night. The doctors quickly learn that she has ovarian cancer and surgically removed one of her ovaries to save her life.
© Photo: Getty ImagesJesse Plemmons
We don't blame you if you don't remember this one! The Breaking Bad and Friday Night Lights actor played a young man named Jake suffering from a bone disorder that leaves him disfigured. Patrick Dempsey's Derek Shepherd is tasked with removing some of the growth, but Jake doesn't make it through surgery.
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