Millie Bobby Brown and Jake Bongiovi are holding on to what they've got.

The Stranger Things actress and the son of Jon Bon Jovi—who announced their engagement in April—recently celebrated another milestone together: his 21st birthday. 

On May 7, Millie penned a sweet message to her leading man, sharing it on Instagram alongside a series of photos with Jake. "this sums us up. In bliss, exploring together," she captioned the pictures, including a shot of them at the Enola Holmes 2 premiere in October. "I am eternally holding your hand. happy birthday fiancé. I love you."

The 19-year-old's celebratory post received a flood of well-wishes from fans and fellow celebs, including Paris Hilton who commented, "So happy for you." 

Millie's Stranger Things co-star Matthew Modine also wrote, "Life is a beautiful long walk. There is a beautiful African saying : if you want to go fast, go alone. If you want to go far, go together. I love you both and enjoy seeing you walk together."

It was just last month that Millie shared her engagement news with fans online.

Quoting Taylor Swift's hit song "Lover," Millie captioned the April 11 relationship announcement, "I've loved you three summers now, honey, I want 'em all." 

And although the couple has received a ton of congratulatory messages on their engagement, there's also been some skepticism, given their young ages.

In fact, Jake's dad even weighed in on the conversation during a conversation with Andy Cohen on May 2. "I don't know if age matters," Jon said on SiriusXM's Andy Cohen Live. "If you find the right partner and you grow together, I think that would be my advice really: growing together is wise. Growing together."

The "Livin' on a Prayer" singer—who also shares kids Stephanie, 29, and sons Jesse, 28, and Romeo, 19, with his high school sweetheart Dorothea Hurley—added, "I think that all of my kids have found the people that they think they can grow together with and we like 'em all."

As for how Jon feels about his son's leading lady? "Millie is wonderful," he noted. "Her whole family is great, really great. Jake is very, very happy."

To see a complete timeline of Millie and Jake's relationship, keep reading!

Millie and Jake enjoyed a day out with her sister Ava Brown, 11, and friends at the Six Flags Over Georgia theme park.

Millie and Jake were spotted out to dinner at Don Angie in New York City's West Village in June 2023, where they were joined by Millie's parents Kelly and Robert Brown. 

Millie announced the couple's engagement on Instagram, quoting Taylor Swift's song "Lover." The two would go on to celebrate with family and friends at an engagement party weeks later.

Jake marked Millie's 19th birthday on Feb. 19, 2023 with a sweet tribute, writing, "Another year around the sun together happy 19th to the girl of my dreams."

The sweet post included photos of the couple.

The pair's silly side is depicted in one image of Jake and Millie clowning around in the pool

Jake and Millie snuggle up in a romantic selfie.

Millie shared photos of the couple in celebration of the New Year, writing, "endlessly in love with the year I've had."

One snapshot showed a photo booth strip of the loved-up couple.

As Millie put it, "grateful for my friends, family, donkey (bernard), my doggies, my puppies teeth, and my partner for life."

Millie and Jake were twinning at the premiere of Stranger Things season four in New York City.

Millie and Jake make their first joint appearance at a celebrity event—the 2022 BAFTA Film Awards in London.

"We're starting a band," Jake wrote on Instagram, "send name ideas."

Jake posted this photo, with the caption, "bff <3"