Mark Large

ABC News' Thea Trachtenberg, Carolyn Durand, John Green and Matt Lombardi report:

To the world, she's Queen Elizabeth II, the beloved British monarch who has reigned for 60 years. But to her grandson Prince Harry, she's just "Granny."

"In a small room with close members of the family, then she is just a normal grandmother.  Very relaxed," the prince said in an interview with ABC News' Katie Couric. "She obviously takes a huge interest in what we all do, that's her children as well as her grandchildren.  She wants to know which charities we're supporting, how life is going in our jobs and such. So you know, she has a vested interested in what we do."

Now, the prince has begun to see his most famous relative in a new light.

"When we were young it was very easy to take our grandmother for granted.  She was just a grandmother to us. It's only really sort of been over the last sort of five, eight to ten years that I've actually really learned to sort of understand and accept the huge deal that she is around the world, especially within the U.K.," Harry said.

To mark the Queen's Diamond Jubilee celebration of her 60 years on the throne, Couric conducted several rare interviews with members of the royal family, TRH Prince Harry, The Duke of Cambridge Prince William and The Duke of York Prince Andrew, which will air in an ABC network special, "The Jubilee Queen With Katie Couric," Tuesday, May 29 at 9 p.m. ET.  The broadcast will also include interviews with Princesses Beatrice and Eugenie and give viewers special access inside Buckingham Palace.

The 27-year-old prince, who is the third in line to the throne, hit the road as his grandmother's royal envoy for the first time this March, visiting the Caribbean, Central and South America to greet and thank her subjects.

The prince attended to royal business on the queen's behalf, but was widely applauded for the fun and charm he brought to the task. He took on Olympic great Usain Bolt in a friendly 20-meter race in Jamaica and boogied with locals in Belize.

To royal watchers, it looked like the prince had not only found his groove, but also his own unique way to express the values of his grandmother, who became monarch when she was only 25.

Watch "The Jubilee Queen With Katie Couric," TONIGHT at 9 p.m. ET on ABC.

While Harry excelled on his first trip, taking on the level of royal responsibility that his grandmother did is something he can't imagine.

"No, not a chance," the prince said on having the queen's duties at such a young age. "But this tour itself has been a brief insight as to what she had to deal with at a very young age … what she's achieved and what she's done and at the age of 25 … confronted with the world's media.  And you can see it in her face now.  You can see it in the way that she parades herself is just immaculate. And she's learned it from all the years of experience."

Sixty years of experience to be exact. And through it all, his grandmother, who is now 86, has shown a remarkable ability to adapt with the times -launching a YouTube page - which Harry says has helped the monarchy endure.

"She's managed to get the family to move with the times, and I think that's incredibly important," he told Couric.  "You can't get stuck in a sort of an old-age situation when everything else around you is changing.  So you have, you have to go with it."

From taking on YouTube to planning for last year's royal wedding, the seasoned royal has shown her adaptability, according to her grandsons. HRH The Duke of Cambridge Prince William said his grandmother urged him to make his wedding to Catherine Middleton his own.

"I was given a list in the first meeting of 777 names, and not one of them on there I knew. So it was a bit daunting and it was like, well, that seems to be the guest list's sorted, but no room for friends or family. And I wasn't too happy about it," Prince William told Couric. "She said, 'Ridiculous. Get rid of the list. Start from your friends.'"

William's nuptials at Westminster Abbey to the Duchess of Cambridge Catherine Middleton was the most-watched wedding in the world, drawing millions of viewers and well-wishers who filled the streets to share in their modern-day fairytale.

As William's brother, Harry said he was nervous at the time.

"I was massively nervous.  Everybody was nervous," he recalled.  "The whole thing was a bit of a blur to be honest because there was God knows how many millions or billions of eyes focused on us. Luckily, mainly those two."

All eyes were on the royal family, but for Prince Harry and William, one important spectator was notably absent from the pews in Westminster Abbey - their mother, the late Princess Diana.

"I think she had the best seat in the house probably," Harry said, admitting it was hard for both brothers not to have their mother there that day. "But yeah, she would have loved to have been there."

Prince William: I'm Sad Princess Diana Never Got to Meet Kate

Prince William also opened up to Couric about his big wedding day and said he tried to prepare himself for his mother's absence, but it was "very difficult."

"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," Prince William said. "It's the one time since she's died, where I've … 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.

"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."

Watch "The Jubilee Queen With Katie Couric," TONIGHT at 9 p.m. ET on ABC.