Middleton speaks candidly in the clip released by the Anna Freud National Centre for Children and Families about childhood mental health.
In the video, the royal encourages young people to talk about their thoughts and feelings.
“Mental health is how we feel and think, things that can’t really be seen but affect us every day,” she says.
Middleton introduces an animated video designed to help begin conversations about mental health in the classroom and beyond.
"It helps us all talk about mental health – what to say and who to talk to when we have feelings that are too big to manage on our own and how to listen and help if one of our friends is finding things difficult," she says.
"Sometimes, it’s just a simple conversation that can make things better."
As The Mail Online reports, the video was filmed in January before, before Middleton is believed to have fallen pregnant.
The royal is suffering from the same acute morning sickness, Hyperemesis Gravidarum, that she experienced with Prince George, now four years old, and Princess Charlotte, aged two, and she has been forced to cancel public appearances as a result.
This article originally appeared on Marie Claire.