"There's wonderful highs and wonderful lows," he said of fatherhood. "It's been quite a change for me personally. I'm very lucky in the support I have from Catherine, she's an amazing mother and a fantastic wife."
"But I've struggled at times," he confessed. "The alteration from being a single, independent man to going into marriage and then having children is life-changing. I adore my children very much, and I've learned a lot about myself and about family just from having my own children. It's amazing how much you pick up just in those moments."
Prince William, who is the older brother of Prince Harry, admitted he's still getting used to "having a girl in the family," as he never had a sister growing up.
"Having a daughter is a very different dynamic," he said. "So I'm [still] learning."
As for Prince George? "[He's] a right little rascal sometimes," the Duke joked. "He keeps me on my toes, but he's a sweet boy."
Now that Prince William is raising a family of his own, a role he says is "wonderful," "fantastic" and "very important," he has a much different outlook on life.
"I worry about the future more," he revealed. "When you have something or someone in your life to give the future to, I think it focuses the mind more about what you're giving them. I would like [my kids] to grow up with more simple aspirations. I think there's a lot of huge aspirations and people living with an enormous amount of stuff that they don’t necessarily need."
"The materialism of the world -- I find quite tricky sometimes," he continued. "I would like George and Charlotte to grow up being a little bit more simple in their approach and their outlook, and just looking after those around them and treating others as they would like to be treated themselves."
As ET previously reported, His Royal Highness was visiting Vietnam to spread awareness about the consequences of illegal wildlife trade, as the Southeast Asian country is one of the main hubs for trafficking wildlife products, including rhino horn, which is used in traditional medicines.
The 34-year-old royal noted that China and the U.S. have already instituted bans on such activities, and that the U.K. is "considering it."
"Ivory treated as a commodity is the fuel of extinction," he told the crowd at the Hanoi Conference on Illegal Wildlife Trade on Thursday. "Ivory is not something to be desired and when removed from an elephant it is not beautiful. So, the question is, why are we still trading it? We need governments to send a clear signal that trading in ivory is abhorrent."
Hear more from his passionate speech in the video below.