There are wedding bells in Luke Hemmings and Sierra Deaton's future!. 5 Seconds of Summer's lead vocalist Luke Hemmings took to Instagram on June 8 to announce that he proposed to longtime girlfriend Sierra Deaton (who he calls by her middle name, Thao) earlier in 2021. "With shaking hands but a full heart I proposed to my best friend earlier this year. I love you Thao and I can't imagine my life without you," he wrote alongside a slideshow of loved-up photos that showed off his fianceé's teardrop-shaped engagement ring. Deaton, who won "The X Factor US" in 2013 and rose to fame in the duo Alex & Sierra with her ex boyfriend Alex Kinsey, also shared the photos and wrote, "it was fun keeping this a secret for so long, but my heart is nearly bursting at the seams. can't wait for forever."