The pair made their relationship Instagram official in 2022.
The happy couple revealed the news on Tuesday's episode of Long's Life Is Short podcast, where Bosworth joined Long and his brother, Christian Long, on the program.
Bosworth and Long admitted that the Vanity Fair Oscars party -- where she flashed her sparkler -- was a "little bit of a debut," but agreed they wanted to share the story of their proposal on a platform that means so much to them, especially after their appearance generated buzz around their new relationship status.
"We just decided that we were going to live our lives, and I'm going to wear the ring, celebrate our love," Bosworth says about the carpet. "And you know there will be photos our there and hopefully people will know, 'Oh, they're taking another step.' But there was a lot of speculation."
Neither Bosworth, 40, nor Long, 44, revealed the exact timeframe of their proposal. However, Long shared that he wanted to pop the question around his now-fiancée's birthday, but that plans changed.
"I did have a special thing planned around your birthday and about a month before that, like, we were talking about life, change and sometimes things happen without warning," Long says.
"It was a moment where it just felt so organic and it felt connected to something very deeply, profoundly personal that we were going through a real-life change," he adds. "So it came out in a very organic way, as all of these moments with you have. Easy wasn't the right word because we were in a struggle, we were in a very difficult thing, but the asking of it was easy and it just kinda spilled out."
"I recall you asking me with a lot of 'clarity' and we had just gone through this hard thing and we had spoken to a therapist and we were trying to move through things at the time," Bosworth shares before going into the proposal details. "And she gave us a really great piece of advice which was: 'Make sure that you're pretty consistently asking the other what you need, or asking the other what they need.'"
She adds, "I remember waking up not so many mornings after that therapy session and I looked at Justin and I said…I remember, I smiled at you, and I said, 'What do you need?' And he, like, really looked at me and he said, 'To spend my life with you.' And I smiled and I said, 'Well, yeah, you have that. Oh my gosh, you have that,' and he said, 'No, I mean I really want to spend my life with you.'"
"It was the easiest, the words just came out, like, so naturally," Long adds.
"I thought it was just the most romantic, honest and loving proposal ... ask to spend one's life with another," Bosworth says.
The couple's engagement comes almost two years after speculation of their relationship began in 2021, and one year after Long confirmed their relationship.
In another segment of the podcast, Long and Bosworth admit the moment they each knew they found the one -- shortly after building a friendship while working alongside each other in House of Darkness.
"In a day I thought, 'I'm going to know this person for the rest of my life and I feel like I've known this person for lifetimes before,'" Bosworth explains. "And that was in a day or two and it already felt well established."
"Yeah, there was this feeling of whiplash, emotional whiplash because we had progressed so quickly in the course of hours," says Long, adding that their relationship has "ease, comfort, safety."
Bosworth took to Instagram to celebrate their announcement with a series of pictures flashing her ring and a message for her fiancé.
"These things are funny to announce. How to do this right? He’s going the distance? I’ve got a Blue Crush? He’s just THAT into me? I’ve won a date with…??? Ok you get it," Bosworth wrote while referencing some of her films.
"We thought it might be nice to share our joy in a conversation you all can listen to, on my future husband’s @lifeisshortpodcast 💛 So if you would like to be in the room with us (sort of!) & hear our story, the link is in my bio. 💍 If life is short, find the one who brings you endless peace and radical wonder. ✨ @justinlong I am so grateful it’s you," she added.
Earlier this month, a source confirmed to ET that the couple was engaged. "They are both thrilled, and their loved ones are incredibly happy for them," the source said. "They make an amazing couple and they're so excited."
This will be Long's first marriage. Bosworth was previously married to Michael Polish, her husband of nearly eight years, before she filed for divorce in 2022.