"It is often said that fathers can often find it hard to talk about their own feelings so there’s no wonder they struggle to speak to their son or daughter about the topic," William wrote. "But we don’t really have a choice."
He noted that a fifth of children will have a mental health issue by their 11th birthday — which could "alter the course of a child's life forever" if left unresolved.
William encouraged fellow fathers to reflect on how they themselves are coping with fatherhood and to "take a moment to ask their children how they are doing" on Sunday.
"And know that if your son or daughter ever needs help, they need their father’s guidance and support just as much as they need their mother’s," William wrote.
Cassandra Vinograd is a Senior Writer and News Editor. Before joining NBC News, she worked as a London-based correspondent for The Associated Press and specialized in politics, foreign affairs and defense.
Vinograd previously worked as an editor for The Wall Street Journal in Brussels and London.
She has reported extensively from Afghanistan and on West Africa and the Middle East.
Emma Ong is a senior desk editor for NBC News in London.