Millie Bobby Brown was about to film Stranger Things season 5 with David Harbour. She and David have been filming Stranger Things since Millie was 11; now Millie is 21. David describes they're relationship as "father-daughter." In interviews, David and Millie said, "We get angry at each other." The claim has not been seen as true or false. David and Millie's relationship has been seen as a heartfelt thing.
David has seen Millie grow up during the show and after the show. He is very fond of their friendship. David and Millie have not talked about this yet. In recent press, they have been supporting each other. (People)