Prince William Interview With Katie Couric

In an exclusive interview with ABC's Katie Couric, airing Tuesday night, Prince William opened up about big wedding day and said it was "very difficult" not to have his mother, late Princess Diana, at his wedding.

"I sort of prepared myself beforehand so that I was sort of mentally prepared . I didn't want any wobbly lips or anything going on," said William, 29. "It's the one time since she's died, where I've . thought to myself it would be fantastic if she was here, and just how sad really for her, more than anything, not being able to see it."

William was 15 when Princess Diana died in a car crash in Paris in August 1997.

"I think she . she would have loved the day and I think, hopefully, she'd be very proud of . of us both for the day. I'm just very sad that she's never going to get a chance to meet Kate."

William's brother Prince Harry was also interviewed by Couric for the documentary to mark the Queen's Diamond Jubilee celebration of her 60 years on the throne.

Harry, 27, who acted as his brother's best man, also felt his mother's absence acutely.

"I think she had the best seat in the house, probably," Harry said. "But yeah, she would have loved to have been there."