William, 37, and his wife Kate, the Duchess of Cambridge, are the parents of Prince George, 6, Princess Charlotte, 5, and Prince Louis, 2.
William spoke about fatherhood with former soccer player Marvin Sordell for a new BBC One documentary, "Football, Prince William and our Mental Health." When Sordell opened up about the impact of growing up without a father and then becoming a father himself, William reflected on the death of his own mother, Princess Diana.
Diana died in a Paris car crash in 1997, when William was just 15 years old.
“Having children is the biggest life changing moment, it really is," William says in the documentary. "I think when you’ve been through something traumatic in life, and that is like you say, your dad not being around, my mother dying when I was younger, the emotions come back, in leaps and bounds."
"Me and Catherine particularly, we support each other and we go through those moments together and we kind of evolve and learn together," he said. "I can completely relate to what you’re saying about children coming along, it’s one of the most amazing moments of life but it’s also one of the scariest."
William has spoken in the past about how he keeps the memory of Princess Diana alive for his kids.
"I think constantly talking about Granny Diana, so we've got more photos up around the house now of her and we talk about her a bit and stuff," William said in a 2017 BBC documentary marking the 20th anniversary of Diana's death. "And it's hard because obviously Catherine didn't know her, so she cannot really provide that level of detail."
"So I do regularly, putting George or Charlotte to bed, talk about her and just try and remind them that there are two grandmothers, there were two grandmothers in in their lives, and so it's important that they know who she was and that she existed," he said.
William has also joked previously that Diana would be a "nightmare grandmother, absolute nightmare."
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"She'd love the children to bits but she'd be an absolute nightmare," he said in a 2017 ITV documentary. "She'd come in probably at bath time, cause an amazing amount of scene, bubbles everywhere, bath water all over the place and -- and then leave."
William said in the same documentary that he has vowed to spend as much time as possible with his children: "I want to make as much time and effort with Charlotte and George as I can because I realize that these early years are particularly crucial for children, and having seen, you know, what [Princess Diana] did for us."
The documentary "Football, Prince William and our Mental Health" airs Thursday in the U.K. at 8:05 p.m. BST, on BBC One.