Taking to her Instagram yesterday, Millie explained how she hurt herself.
"Hi guys. So another milestone in my life," Millie began in the video. "I’ve never actually broken a bone except for now. I have split my kneecap."
She explained how her doctor told her to "rest up."
Millie is nominated in this year's Best Performance in a Show category, so she also took the time give her Stranger Things costars Gaten Matarazzo, Caleb McLaughlin, Finn Wolfhard, Sadie Sink, and Noah Schnapp a shout out.
"I hope Gaten, Caleb, Finn, Sadie and Noah have the best time," she said. "And I love them so dearly, so I wish you guys the best and I’m sending my luck with you. And I’ll be there in spirit." Millie ended her video by saying: "Love you guys so much and peace out."
But that's not all she's nominated for!
Stranger Things is up for Best Show, Finn and Millie are up for Best Kiss, Noah is nominated for Most Frightened Performance, Dacre Montgomery received a nomination for Scene Stealer, and the entire group is up for Best On-Screen Team.