5SOS: Luke Hemmings is engaged to his long-term girlfriend Sierra Deaton

5 Seconds of Summer frontman Luke Hemmings has announced his engagement to long-term girlfriend Sierra Deaton. The western Sydney native actually popped the question months ago, but waited until this week to share the news publicly with fans. While he didn't reveal details of their engagement, Sierra said they had celebrated Vietnamese New Year together, hinting Luke may have proposed on February 12. In love: The western Sydney native actually popped the question months ago, but waited until Tuesday to share the news publicly with fans Lovers: While he didn't reveal details of their engagement, Sierra said they had celebrated Vietnamese New Year together, hinting Luke may have proposed on February 12 'It was fun keeping this a secret for so long, but my heart is nearly bursting at the seams.