I didn't really plan it that far in advance... I wanted it to mean something, other than just the act of getting engaged
According to William, he hadn’t planned the proposal – which took place in Kenya in 2010.
He says: 'I didn't really plan it that far in advance, like I just knew I wanted it to feel comfortable where I did it and I wanted it to mean something, other than just the act of getting engaged.
The Prince added: ‘She understands what it means to me being in Africa, and my love of conservation.'
The documentary will also see Prince William open up about how his perspective has altered since becoming a father.
He says: 'Suddenly you start thinking of like, wow, there is stuff you want to safeguard for the future. I've always believed it, but to actually really feel it as well, it's coming through powerfully now as well.'
The documentary will also feature exclusive footage of the Duke and Duchess of Cambridge's first public appearance since the birth of their son George in July, as the pair will attend the Tusk Conservation Awards in London on Thursday evening, where Prince William present the award for Conservation In Africa.
New Father, New Hope airs on ITV this Sunday at 6pm