"It's been 14 months since Miley Cyrus and Liam Hemsworth last cozied up to each other on the red carpet -- not too surprising, given their volatile history. Even so, the on-again couple made a joint appearance in L.A. on Thursday, Aug. 8, at the premiere of Hemsworth's new film, Paranoia. Hemsworth, 23, suited up in head-to-toe BOSS, while Cyrus, 20, modeled a Proenza Schouler dress and Celine heels. Despite putting on a united front, a source tells Us Weekly the hot-and-cold couple were anything but lovey-dovey. "Miley and Liam acted like they didn't even know each other the entire night," the source says. "She was wearing her ring but they acted as if they were strangers." PHOTOS: Are Miley Cyrus and Liam Hemsworth meant to be? Cyrus gave Hemsworth a few quick kisses, the source notes, but "they were awkward and he didn't seem into them." Tellingly, the Australian actor ignored questions about the "We Can't Stop" singer on the red carpet -- though he did admit he's not one to say much about his love life. "On Twitter, I don't share anything personal. I try to keep as much of my personal life to myself. I don't feel the need to go out and show the world what's happening in my life every second," he said. "I think it's a good chance to connect with fans and give fans an inside look on films you do. I think it's great for that kind of thing, but it's very new to me." PHOTOS: Miley Cyrus' hair evolution Hemsworth asked Cyrus to marry him in June 2012 with a 3.5-carat diamond ring; the Last Song costars briefly called it quits earlier this summer. "At first they were yin and yang, balancing each other out," a source told Us at the time. "But they got more and more out of sync." PHOTOS: Miley Cyrus' raciest outfits ever The actor's famous brothers, Chris and Luke, even staged an intervention. "Liam's loved ones think he needs someone more stable," a pal told Us in June. Another source added, "Liam's brothers had heart-to-hearts with him because they were worried. Each time, he was more receptive." PHOTOS: Miley Cyrus' wild life in the public eye When Cyrus began promoting her upcoming fourth album, she implied that their bad days were behind them. When asked if she's still planning to marry Hemsworth during a June 26 appearance on Good Morning America, she cheekily replied, "I'm wearing a ring, so. . ." This article originally appeared on Usmagazine.com: Miley Cyrus, Liam Hemsworth Acted Like "Strangers" at Paranoia Premiere"