"[I wrote it] on the way to 'The Voice,'" she shared. "I drive myself everywhere, but that day I decided to Uber, and I was trying not to sing out loud because someone else was in the car."
"They're going to talk about me if I come out of restaurant with Liam. So why not put the power back in my relationship and say, 'This is how I feel?'" the star added of the personal song.
"Malibu" will debut May 1 ahead of Cyrus' sixth studio album.
The singer, who last released Miley Cyrus & Her Dead Petz in 2015, couldn't help but gush over Hemsworth in a birthday post in January.
"Happiest birthday EVER to my favorite being EVER EVER EVER! You have been my best friend since the day we met..... I am beyond lucky to share sooooo many animals with you!!!" she wrote of their many pets.
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