The "Something Beautiful" singer-songwriter said Morando, the drummer for the band Liily, surprised her and got down on one knee while the couple were on a recent trip to Japan.

"I am not easy to surprise, because I love to control every situation. And I had completely surrendered," Cyrus told ABC News' Chris Connelly. "I actually had never gone to Japan, which, I did that purposefully. I wanted one place in the world that could be my special place that I saved for me."

Cyrus, 33, and Morando, 27, are taking the next step after four years of dating. Cyrus said everything is unfolding at the right time for her amid the release of her new song, "Dream As One," for the upcoming film "Avatar: Fire and Ash," from 20th Century Studios and Lightstorm Entertainment.

"My life has been perfectly aligned with the release of 'Avatar,' my personal life -- those two things kind of, I guess you could say, marrying each other and harmonizing with one another," she said.

She called Morando a "great partner" and credited him with supporting her personal growth in the last few years.

"Me and Max have been together for four years, and it's very obvious the drastic amount of growth that I've had in those four years ... and that really, a lot of that is because I have a great partner," said Cyrus. "You just want to dream the biggest you can, and you want to have someone by your side that always tells you you can do it."

Cyrus showed off her engagement ring and added that Morando "did good" with the selection.

After their engagement and return from Japan, Cyrus said she jumped straight into working on "Dream As One" for the "Avatar: Fire and Ash" film.

"When I came back home, I went straight into 'Avatar' world. People think of it as a film that's larger than life. It's this grand scale, but actually at the heart of 'Avatar,' it's really about relationships, love, having each other's back," Cyrus said. "And so it actually felt very aligned with my life."

In "Dream As One," which she co-wrote and co-produced with Andrew Wyatt and Mark Ronson, Cyrus writes and sings about an enduring love, a theme mirrored in her own personal life.

"It's pretty unbelievable to have something that feels almost like a journal entry [with] something as large scale as 'Avatar,'" she said. "I was able to watch the film. I understood the trials of each character. But [director James Cameron] just really wanted it to feel like the way that I always write a diary entry."

Cyrus' "Dream As One" is available to download and purchase now.

"Avatar: Fire and Ash" is out in theaters Dec. 19.