Prince William shares how the Queen helped plan his wedding

(CBS) Prince William and Kate Middleton had a lot of help planning their lavish April 29, 2011, wedding - but the prince said some of the most valuable advice came from his grandmother.

In an interview with British journalist Robert Hardmann for his book "Our Queen," excerpted in the Daily Mail, William revealed the advice Queen Elizabeth II gave him about the wedding guest list.

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"I was given this official list of 777 names - dignitaries, governors, all sorts of people - and not one person I knew," William said in the interview.

So he went to his grandmother for advice.

He recalled, "I rang her up the next day and said: 'Do we need to be doing this?' And she said: 'No. Start with your friends first and then go from there.' And she told me to bin the list."

"She made the point that there are certain times when you have to strike the right balance," he added. "And it's advice like that, which is really key, when you know that she's seen and done it before."

But, he revealed, the monarch wasn't flexible on everything - she was adamant that he wear his Irish Guards uniform for the ceremony.

"So you don't always get what you want," he said, "put it that way."

William said of his relationship with his grandmother: "I say to people, 'She's my grandmother to me first and then she's the Queen.' Words that come from her, I take very personally and I really appreciate...My relationship with my grandmother has gone from strength to strength."

As the queen nears her Diamond Jubilee, celebrating 60 years on the throne, she has no intention of cutting back on her duties, said William.

"We do hint at taking some things off her, but she won't have anything of it," he said. "She's so dedicated and really determined to finish everything she started. She'll want to hand over knowing she's done everything she possibly could to help, and that she's got no regrets and no unfinished business; that she's done everything she can for the country and that she's not let anyone down -- she minds an awful lot about that."

William also added that he tries "desperately hard" not to think about his own future as the king of England.

"As I'm flying along in my helicopter through the mountains of Wales, I try desperately hard not to think about it. That can wait until I'm a bit older," he said.

Hardmann's book will be published in the U.K. on Oct. 6, and in the U.S. this spring.