Now, in her latest Instagram posts, the British actress - who has been promoting new film The Electric State - slipped into fun and flirty looks calling back to the Y2K era.
Many social media users were stunned by Millie's age, however, and observed how she appeared to look decades older.
The actress, 21, was the epitome of elegance in a peach-coloured satin gown that clung to every inch of her svelte frame.
Millie Bobby Brown, Mikey Madison and Timothée Chalamet were among the stars posing for pictures.
Millie Bobby Brown took a moment to relax after ringing in her 21st birthday with husband Jake Bongiovi and friends in Turks and Caicos.
Millie Bobby Brown has revealed the dark side of child stardom after joining Stranger Things aged 11.
Fans brought up the relationship after Kendrick's Super Bowl half-time show, where he ended the concert with Not Like Us, a song that
The Stranger Things actress, 20, was seen modelling for her fashion and beauty brand Florence by Mills' Valentine's Day collection, The V-day Edit.
Millie Bobby Brown has revealed her jaw-dropping new hairstyle, as she bid farewell to 2024 with a glamorous new transformation.