The pair first met while filming The Last Song, but only began dating after the film wrapped production.
Hemsworth and Cyrus were believed to have ended their relationship last autumn, but the 'Party in the USA' singer hinted just two months that she and the Knowing star had reunited.
Cyrus's older brother Trace, 22, has now seemingly confirmed that the popstar and Hemsworth are once again seeing each other, disclosing to Us Weekly that he believes his sister is truly happy with the Australian actor.
He added: "I support my sister in anything she does."
Trace, a guitarist and singer for the band Metro Station, also revealed that the Cyrus family have put aside any past squabbles aside and are united in their support for one another, saying: "We're tight, so that's all the matters. Life is good, so I can't complain."
So Undercover, Miley's next film, is to be released in October in US cinemas.
Watch the Miley Cyrus 'Party in the USA' music video below: