Cyrus, 16, recently completed filming new movie The Last Song with Aussie Hemsworth and was rumored to have grown close to her on-screen love interest throughout the shoot.
Speculation of a romance with Hemsworth, 18, rocketed when the star was reportedly spotted kissing him goodbye at Nashville Airport in Tennessee last month.
Cyrus has since denied reports of a relationship with Hemsworth -- but the actor's ex-girlfriend has now come forward, accusing the Hannah Montana actress of wrecking their five-year romance.
Laura Griffin, 19, claims Hemsworth flew back to Australia last month and broke up with her -- and she is blaming Cyrus for the split.
She tells Australia's Woman's Day magazine, "He was my boyfriend and my best friend. There is no other reason why we would have broken up."
Griffin also reportedly posted a message on her Facebook page about the break-up, writing, "Liam and I have been inseparable since school. But it's Miley Cyrus! How can I compete?"
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