Prince William didn't want his mother's death to "break" him.
The 35-year-old royal was devastated when Princess Diana tragically passed away in August 1997 when he was just 15 but he was determined not to let her untimely passing affect him so badly that it would ruin her "legacy".
Speaking to the BBC for the Diana, 7 Days documentary, he said: "When you have something so traumatic as the death of your mother when you're 15, as very sadly many people have experienced and no one wants to experience - it'll either make or break you. And I wouldn't let it break me. I wanted it to make me.
"I wanted her to be proud of the person I'd become. I didn't want her legacy to be William or Harry were completely and utterly devastated by it and all the hard work and the love she put into us when we were younger, for it to go to waste."
Meanwhile, Prince Harry previously admitted he had "no sudden outpouring of grief" when he was told his mother had died.
He said: "One of the hardest things for a parent to have to do is to tell your children that your other parent has died. But he [Prince Charles] was there for us, he was the one out of two left and he tried to do his best and to make sure we were protected and looked after. But, you know, he was going through the same grieving process as well."
Whilst William added: "I remember just feeling completely numb. And you keep asking yourself, 'Why me?' all the time. 'What have I done?'"