19-year-old Millie is currently dating Jake Bongiovi, the 21-year-old son of Jon Bon Jovi.
In April 2023, the actress announced they were engaged, posting a sweet picture of the loved-up couple on Instagram. "I've loved you three summers now, honey, I want 'em all," she captioned the post.
"I've always loved that ring. It always stuck out to me, so she gave it to Jake. They were in cahoots about the whole proposal," she told The Sunday Times, adding, "I love that I can always keep a piece of my mum with me."
During an interview with Wired she revealed how the couple met, and it's straight out of a Gen Z love story.
"We met on Instagram," she explained. "And we were friends for a bit, and then, what can I say?"
"I was interested in him and wanted to know more. As soon as we spoke I knew he was going to be a huge part of my life," she told The Times. "I ran to my mum and said, ‘I really, really like him!' After we met we knew we never wanted to leave each other's side."
"You can't pinpoint why, it's just the feeling of knowing that that's the person you want to spend the rest of your time with," Millie reflected when asked how she can tell whether someone is 'the one.'
"I think so much of life is overthinking. The one thing that made clear sense to me was him."
The pair first sparked romance rumours in June 2021 when they were photographed together in New York, a month later they made their Instagram debut on each other’s accounts.
The couple made their red carpet debut together at the 2022 BAFTAs on March and recently attended the premiere of Enola Holmes 2.
The couple isn’t shy about their relationship, with both of them regularly sharing photos on Instagram.
Following the fourth season of Stranger Things, Jake publicly shared his support for his girlfriend writing on Instagram, "Congratulations babe u deserve the world love you."
Millie also shared pictures of their European vacation in May this year alongside the caption, “te amo” which translates to I love you.”
Despite Millie and Jake’s relationship going strong, the actress recently set the record straight on her relationship with Stranger Things co-star, Noah Schnapp.
"We were always able to kind of connect with each other,” she explained, before describing their relationship as "so platonic, which is so beautiful."