"Happiest birthday EVER to my favorite being EVER EVER EVER!" the 24-year-old captioned a pic of the couple on Instagram. "You have been my best friend since the day we met..... I am beyond lucky to share sooooo animals with you!!! I love you @liamhemsworth."
In the snapshot, Cyrus and the Independence Day: Resurgence actor are making silly faces for the camera.
The couple first met on set of 2010's The Last Song and got engaged two years later. They split in 2013, but reconciled in 2015. In October, they made their first joint appearance in three years when they attended Variety’s 2016 Power Women luncheon in Beverly Hills.
Back in May, Hemsworth opened up about the couple giving their relationship a second shot during an interview with GQ Australia. "Of course it was hard, man. But we were both going in different directions and it's just what needed to happen. We were both super young and it was a good decision at the time — we both needed that," he said at the time. "I guess when I feel something, then I just feel it and I go for it. I make my decisions about what's going to make me happy, what I think is right and what I want to do — and I don't worry too much outside of that."
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