Miley Cyrus' new song 'Malibu' is inspired by her fiancé Liam Hemsworth.

Liam Hemsworth and Miley Cyrus

Liam Hemsworth and Miley Cyrus

The 24-year-old singer has revealed that her first single since 2013 was written over a year ago and is about her falling in love with the 27-year-old actor and how she wouldn't be "happy" without the 'Hunger Games; star in her life.

She said: "It's kind of ... I mean, I definitely would be lying if I didn't say that was the influence of the song.

"The single says, 'I never stopped by the shore, under the sun with my feet in the sand, but you brought me here and I'm happy you did, because now I'm as free as birds in the wind, because I wouldn't be here if it wasn't for you, but what I found here is through me and what I needed.'"

The 'Wrecking Ball' singer said she has completely "changed" as a person for the better.

Speaking to Australian radio hosts Kyle Sandilands and Jackie 'O' Henderson on Thursday (11.05.17) morning's 'Kyle And Jackie O Show', she admitted: "The way I think, the way I dress, the way I sound. People make 'you've changed' a derogatory statement, I take it as an amazing compliment.

"You should always be changing, you should always be growing up, you should always be evolving. The one thing you can always count on is change."

Miley admitted that she is in a much happier and content place than she was four years ago.

She said: "Just four years ago I was sliding down my own tongue, and now you know I'm frolicking on the sand and in the fields."

And, that is partly due to her stopping taking drugs.

Billy Ray Cyrus recently said his daughter has a "joy for life" now that she's stopped smoking marijuana.

He said: "As a dad, I see Miley really just functioning on, like, a figure and a joy for life. I don't know how to break it down more than just the fact that I see a joy in her spirit and something coming from within that is just pure beauty, if you will.

"I think she just found ... she's firing off all cylinders. Her thoughts, her instincts, everything is at the top of its game. Sometimes you have to clear out the junk. And then you realize what's most important. Whatever is going on, it's working for her."