25 Celebrities You Forgot Guest Starred on 'Grey's Anatomy'

Before many of your favorite stars became household names… they were on Grey’s Anatomy.

The beloved ABC series has been on the air since since 2005 – almost 15 years – and is currently in its 16th season.

Stars like Demi Lovato, Millie Bobby Brown, and Mandy Moore have all made cameos on the show.

We’ve rounded up 25 celebrities whom you might have forgotten had guest-starring roles.

Season 16 of Grey’s Anatomy returns on January 23!

READ MORE: Ellen Pompeo Reveals Her Ideal Ending for ‘Grey’s Anatomy’!

Click through the slideshow to see which celebs you forgot guest starred on Grey’s Anatomy…