The 18-year-old looked stunning in a white satin gown with a black mesh shoulder and high-leg split next to her 20-year-old boyfriend, the son of Jon Bon Jovi.
Millie was joined by her Stranger Things co-stars including Winona Ryder, Finn Wolfhard, Noah Schnapp and Natalia Dyer, all looking equally as glam.
Maya Hawke and Natalia donned black gowns, while Winona opted for a three-piece suit as she posed with her boyfriend Scott Mackinlay Hahn.
Following in Winona’s footsteps, Sadie Sink, 20, chose an elegant white suit, while posing with co-star Gaten Matarazzo, 19, who wore a multi-patterned pink suit.
Millie looked stunning in a white gown with boyfriend Jake by her side (Picture: Getty)
We can’t wait for the new series! (Picture: Erik Pendzich/REX/Shutterstock)
Millie debuted her new blonde locks (Picture: Getty)
The Hawkins gang back together! (Picture: Getty)
The three other members of the Stranger Things Hawkins gang, Finn, who plays Mike Wheeler, Noah, who plays Will Byers, and Caleb McLaughlin, who plays Lucas Sinclair, also looked chic in suits, with Caleb sporting a dalmatian print with snakeskin boots.
David Harbour, who plays Jim Hopper, attended with wife Lily Allen, and posed with Millie on the red carpet in a sweet pic of the two hugging.
David wowed in a unique Stranger Things suit, with imagery of the Netflix series embroidered onto his piece.
The premiere comes ahead of Stranger Things season four dropping on Netflix in a few weeks.
David sported an incredible Stranger Things suit (Picture: WireImage)
The pair shared a sweet hug (Picture: Cindy Ord/Getty Images)
An iconic pair (Picture: MediaPunch/REX/Shutterstock)
The thrilling sci-fi series will follow a new ‘war’ for Eleven and the rest of the Hawkins gang, and, nearly three years since the last season, this time around it looks to be just as scary as we’d expect, with a new gruesome villain known as Vecna.
Millie previously admitted that this season was ‘the hardest to film.’
‘This has definitely been the hardest season I’ve ever filmed,’ she told Collider.
Winona was accompanied by Scott Mackinlay Hahn (Picture: WireImage)
Finn Wolfhard plays lead character Mike Wheeler (Picture: MediaPunch/REX/Shutterstock)
We love the dalmation! (Picture: Getty)
‘And there have been some of the scariest things that I’ve ever seen as a human, which you guys will get to see for sure.
‘I’ll get to tell more stories and touch on my experiences as a person filming on the set with these legitimate scary things.’
More: Stranger Things
Millie and Jake went Instagram official in November 2021, and since then the pair have been dipping in and out of social media sharing their romance with their millions of fans.
Stranger Things season 4 part 1 will be available to stream on Netflix from May 27.
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Entertainment – Metro