In August, Cyrus, 60, popped the question at his farm in Franklin, Tennessee, where Firerose, 34, had moved to earlier in the summer.
"Billy looked at me and said, 'Do you, do you wanna marry me?' And I was just like, 'Of course I do. I love you,'" Firerose said. "He said, 'I love you. I wanna make this official. I wanna be with you forever.'"
While proposing to the Australian singer, the "Hannah Montana" star didn't get on one knee, and there was no engagement ring. However, Firerose noted that she later chose her own ring, which she also designed.
Cyrus went on to open up about his romance with Firerose, revealing that the two first met over a decade ago on the set of "Hannah Montana." The "Old Town Road" singer sweetly credited his late German Shepard pup, Tex, for introducing him to Firerose.
"I loved doing that show," he said of "Hannah Montana. "There's a couple old pine trees on the lot that look like Tennessee. Tex and I would go out there in the middle of the day and he'd take care of his business and we'd stretch and I'd think how much I missed Tennessee. On that given day, Firerose came out of the front door. There was almost a moment of, I don't know, recognition. I was like, 'This girl's a star.'"
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Cyrus said Firerose greeted him and Tex, and shared that she had an audition, which she admitted she can't recall what it was for, but knows she didn't get the part.
"She told me she'd had an audition and I said, "Well, I'm sure you got the job,'" Cyrus told People. "I just thought, well, the casting agents, the producers, the writers, they're all on the floor of where we do 'Hannah Montana.' And I actually said to her, 'Don't ever take a strange man up on this offer, but, in this case, Tex will testify that you will be totally safe. I'm going to introduce you to a producer and you can kind of make yourself at home and watch us rehearse and you know, maybe it might lead to a role or just another contact at Disney.'"
He added, "And so, off me and her and Tex went back to the studio and I think she met a lot of the cast and met the producers, writers. And, in some ways, well, in a lot of ways, we became friends."
The two kept in contact. Firerose shared that their "friendship was so solid over the years," while Cyrus gushed over his fiancée's talent. "She plays all of her own instruments and writes her own songs. We began sharing music, and it just evolved."
The couple dropped their first song together in July 2021, with Firerose noting that she became a support system for Cyrus, who lost his mother, Ruth Ann Casto, four months after he and his ex-wife Tish Cyrus divorced.
"Billy confided in me a lot of what was going on in his life," Firerose said. "I was just the best friend I could possibly be, supporting him."
Tish filed for divorce from Cyrus in April, with People noting that the former couple's divorce has since been finalized. Following the split, Cyrus said moving forward "took a lot of prayer. A lot."
However, during the pandemic, he grew closer to Firerose, whom he described as a "light of positivity."
"There was sickness and death, and hard times," Cyrus told People. "All of the sudden, the life that I've always known as a touring artist didn't exist anymore. A moment of so much change. And at the same time, Firerose, who had been such a light of positivity, such a best friend."
He added, "And then when we began sharing the music, it just evolved more into, as musical soulmates, to soulmates, happy, pure love that to me, I didn't know could exist. Again, we're musicians, first and foremost, both of us. And we found this harmony, and this rhythm, this melody to life."
The "Bad Man" singer said he's finally in a time of "good" after experiencing a period of "bad."
"I've spent my life worried about things that are beyond my control. But at this spot in my life, knowing that all you really have is the happiness that you feel inside your mind and your heart ...," he told People, before getting emotional. "Finding Firerose and getting engaged and then losing my mom [a few weeks later]—see? The teeter-totter will not stay in the middle," he says. "But having somebody to ride it out with now -- that's giving me a little more balance."
Meabwhile, also during the interview, the country singer denied reports that there is bad blood between himself and his children. Cyrus is dad to six kids, including the five children he shares with Tish: Miley Cyrus, 29, Brandi, 35, Trace, 33, Braison, 28, and Noah, 22.
"Everyone knew that that relationship was over a long time ago," he said about his marriage to Tish. "Everybody's turning the page. It's been a lot, but everyone knew that it was time for a change."