"I've never gotten along with someone so well," the singer and actress, 16, tells Seventeen for its December/January issue, out Nov. 24. "I was a little anxious about making this movie; I wanted everything to be perfect. To go on set and feel insecure was a totally new element for me. But he felt the same way. He admitted his insecurities, and it was really nice to have someone who understands me for once."
The two, who are starring together in The Last Song, have already been spotted making out off the set, but Cyrus, who was last linked to an on-off boyfriend known as Nick Jonas and model Justin Gaston, has refused to divulge the exact nature of her relationship with the 19-year-old actor.
But it's clear Hemsworth has a lot of sway over Cyrus' life, including encouraging her recent and sudden withdrawal from Twitter.
"It sucks when your personal life becomes public," she says. "So I'm finding ways to make my personal and private life more of my life – which is one of the reasons why I deleted my Twitter. We've decided that any type of relationship that we have, we will always just keep it very D.L. First and foremost, we are best friends, so that's what I tell people all the time."
She also thanks Hemsworth for the notable changes she's gone through in recent months, including several statements that have her tween fan base in a confused tizzy – such as letting go of Twitter, deriding popular music, and spurning the Twilight phenomenon.
"Liam has been a big part of that," she says. "All you want is for one person to say, 'You did a really good job today.' Or 'You look really beautiful,' or 'I was really moved by that.' You just want one person to make you feel good about something you're doing."