Prince Harry has been dedicated to charity work for many years now, but he also knows that having a bit of fun can be the best way to get more people involved. The royal showed off his sweet smile in a newly released video for his family's charity initiative Heads Together over the weekend, in which he tries to encourage people to join his team in the upcoming 2017 London Marathon. "Everyone runs the marathon for a different reason and for fantastic causes," he says. "If you already have a place and are undecided for who to run for, William, Katherine, and I would like to invite you to run with Heads Together . . . Together, we can start the biggest ever national movement to end stigma on mental health and change the conversation for everyone." As he whips out his blue sweatband at the end, though, he can't help but laugh at himself as he lets out a small giggle. This isn't the first time the royal family has tried (and failed) to keep a straight face during one of these promos, and we love them for it.