William, now 37, makes the acknowledgment in a documentary on football and mental health, set for release Thursday.

The prince describes how Diana’s death in a 1997 car crash in Paris was “traumatic” for him and how being a father had sometimes been “overwhelming” as the memories came flooding back, the Times of London reported.

“Having children is the biggest life-changing moment, it really is,” he said “I think when you’ve been through something traumatic in life . . . my mother dying when I was younger, the emotions come back, in leaps and bounds.”

William sees fatherhood as “a very different phase of life — there’s no one there to help you, and I definitely found it very, at times, overwhelming. Emotionally, things come out of the blue that you don’t ever expect or that maybe you think you’ve dealt with,” according to the Times.

He tells his three children — Prince George, 6; Princess Charlotte, 5; and 2-year-old Prince Louis — “constantly” about Diana.

“It’s important that they know who she was and that she existed,” he said.