"We're homies," Trace, 22, told Us Weekly Thursday of his friendship with Hemsworth, 21. "I support my sister in anything she does."
Miley, 18, began dating The Hunger Games' Hemsworth in late 2009 when they costarred in The Last Song; they broke up the following August, though they were spotted making out in Cyrus' Mercedes Benz SUV one month later.
"Everything is good," the former Metro Station rocker said during the Billabong Design for Humanity Event in Hollywood. "We're tight, so that's all the matters. Life is good, so I can't complain."
Trace, who currently fronts the band Ashland HIGH, added that his sister recently recorded a song for his next album. "The song with Miley is called 'Shot in the Dark.' It will be out soon," he teased. "It will be a single for sure!"