The actress, who stars as Eleven in the Netflix sci-fi drama, is seen with curly hair as opposed to her usual buzz cut, which she sported throughout the first season.
The picture, which appears on the cover of Entertainment Weekly, also features Millie's co-stars Finn Wolfhard, Noah Schnapp, Gaten Matarazzo and Caleb McLaughlin.
The 12-year-old shared the image with her 2.6 million Instagram followers, captioned: "Hey guys! @entertainmentweekly did a First Look at Season 2! This is all we can share.. for now.. #strangerthings #elevenisback."
Predictably, the post generated a great deal of interest and in particular from Eleven's new look.
Stranger Things star Millie Bobby Brown revealed a first-look image of season two
A photo posted by Millie Bobby Brown (@milliebobby_brown) on Feb 8, 2017 at 9:48am PST
At the end of the first season, Eleven disappeared with fans left wondering whether she had died or if she had been banished to the Upside Down.
In the last scene, El seemingly sacrificed herself to defeat the Demogorgon.
However, as she appears reunited with her friends on the cover, could it be that El is in fact alive and well?
Stranger Things: Eleven usually
Actress Millie Bobby Brown in pictures
Fri, December 16, 2016
Stranger Things actress Millie Bobby Brown, the British schoolgirl who has taken Hollywood by storm.
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Stranger Things actress Milly Bobby Brown in pictures
Creator Matt Duffer has kept tight-lipped on the upcoming series.
He has merely said that the new episodes will “explore the repercussions of everything that happened” to Will, Eleven and the rest of the gang.