Royals See Princess Kate's Emotional Cameo in Mental Health Documentary: 'You All Are Heroes' Princess Kate is headed to the small screen! By Erin Hill Erin Hill Twitter Senior News Editor, PEOPLE People Editorial Guidelines Published on April 12, 2017 11:46 AM Share Tweet Pin Email Princess Kate’s passionate efforts to raise awareness around the issue of mental health are taking her to the small screen. As Kate, Prince William and Prince Harry gear up for the upcoming London Marathon on April 23, they’ll also appear in “Mind over Marathon,” a two-part documentary airing on April 20 on BBC One that follows a group of 10 runners affected by mental health issues as they prepare to run the big race. The runners are taking part in the London Marathon with Heads Together, the charity campaign led by the royal trio. The documentary follows the group of runners as they prepare for the race. In the documentary, the royals join them at one of their training sessions to talk to each of them about the mental health challenges they have faced and their preparation for running the marathon. RELATED VIDEO: Princess Kate and Prince William Highlight Mental Health on Last Day in Canada In a moving clip, Kate tells the runners, “You all are heroes.” William is set to attend a special screening of the documentary on April 18, and all three royals will be at the big race on Sunday, April 23, to cheer on the runners.