The young Australian actor has been dating Cyrus for two and a half years after they met on the set of The Last Song in 2009.
"What happened happened, and we've been together two and a half years," Hemsworth said. "She makes me really happy. When you start, you want to be professional, but when you're filming those scenes with someone and pretending to love them, you're not human if you don't feel something."
Cyrus previously caused controversy after a private video at her 19th birthday was released in November. The former Hannah Montana star was seen telling her guests that she smoked "way too much f**king weed" and joking about a Bob Marley-themed birthday cake.
Hemsworth addressed the incident, saying: "She's in a room full of her best friends. And you have one person who comes in there and videos it. The poor girl can't have one night where she can feel safe in her own world. It's ridiculous."
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"What happened happened, and we've been together two and a half years," Hemsworth said. "She makes me really happy. When you start, you want to be professional, but when you're filming those scenes with someone and pretending to love them, you're not human if you don't feel something."
Cyrus previously caused controversy after a private video at her 19th birthday was released in November. The former Hannah Montana star was seen telling her guests that she smoked "way too much f**king weed" and joking about a Bob Marley-themed birthday cake.
Hemsworth addressed the incident, saying: "She's in a room full of her best friends. And you have one person who comes in there and videos it. The poor girl can't have one night where she can feel safe in her own world. It's ridiculous."