Millie Bobby Brown
The Stranger Things star was actually around 11-years-old when she appeared on an extremely dramatic episode during season 11. She plays 11-year-old Ruby who calls into the hospital because her mom stopped breathing. Eventually she's taught over the phone how to make a clean air way for her mother, which then caused her heart to stop beating. In a dramatic twist, Ruby's phone dies and keeps her mom going until help arrives.
Faye Dunaway
The legendary actress showed up in season 5 as Dr. Margaret Campbell, an old-school doc who tends to disagree with other Seattle Grace surgeons.
Mandy Moore
Before she was filling tear ducts as Rebecca Pearson on This Is Us, Moore appeared in four episodes of the show as Mary Portman, a patient who survived the gruesome shooting at Seattle Grace Hospital.
Demi Lovato
The "Confident" singer acted in one episode during season 6. She played a teenager named Haley May who tried to rip her own eyes out. She left the episode with both eyes intact and was cured after an inner ear surgery.
Zach Gilford
Zach Gilford traded in his Friday Night Lights quarterback apparel for some army gear during season 5 of the show when he played a soldier looking to recover.
Leslie Grossman
The American Horror Story actress showed up in one episode during season 5.
Kyle Chandler
Clear eyes, full hearts, another Friday Night Lights star? Can't lose with that. Chandler, who played Coach Eric Taylor on the hit show, acted in four episodes of Grey's as bomb squad chief Dylan Young. He was there that fateful episode when someone walked into the OR with a bomb.
Sarah Paulson
Another AHS alum is in the house (hospital). Paulson played Meredith's mom, Dr. Ellis Grey, in a flashback episode during season 6.
Elisabeth Moss
The Handmaid's Tale star showed up towards the end of season 3 when she played Nina Rogerson. It happened around the same as her debut as Peggy Olson in Mad Men.
Jesse Plemons
Plemons, who also happened to be on Friday Night Lights, was in one episode in season two.
Matt Lanter
Lanter, who played heartthrob Liam on 90210, had a brief stint in an episode during season 4.
Scott Foley
Before Foley appeared on another Shondaland show, Scandal, he played dying patient Henry Burton in 15 episodes during seasons 7 and 8. He married Dr. Teddy Altman.
Christina Ricci
Ricci and Kyle Chandler overlap as cameos in the two scary episodes where someone walks into the OR with a bomb. Ricci played the paramedic who prevented the bomb from detonating.
Leslie Odom Jr.
Pre-Hamilton fame, Odom Jr. performed in an episode of season 5 where he resentfully donates his kidney to his father.
Josh Radnor
Radnor of How I Met Your Mother fame will make his appearance on the show as Meredith's love interest, although it may be brief. The two are going on a blind date, so it remains unclear as to how long his run on the show. Love is blind?