Kevin also took to Instagram to gush about his firstborn, writing, "Happy birthday my beautiful girl we love you so much Alena!" Meanwhile, the Jonas brothers' dad, Kevin Jonas Sr., also shared a flashback pic of the birthday girl.
"Happy Birthday to our special little angel Alena. Glammy and PawPaw Love you so much!," he wrote.
The brothers recently reactivated their Instagram account, which had fans freaking out and speculating a JoBro reunion. While Nick took notice of fans' reactions, none of the guys have said anything about a possible reunion.