London - Prince William has revealed his grandmother, Queen Elizabeth II, is an "important" part of his life who gives him invaluable advice.
The 29-year-old royal - who is second in line to the British throne after his father Prince Charles - has a close relationship with the monarch and feels he can ask her any question.
As he has gotten older and his role as a member of the Royal Family has increased William - who married Kate Middleton in April - needs her advice more and more.
In an extract from new book Our Queen by Robert Hardman, he said: "My relationship with my grandmother has gone from strength to strength. As a shy, younger man it could be harder to talk about weighty matters. It was, 'This is my grandmother who is the queen, and these are serious historical subjects.'
"As I've got older, she's become an even more important part of my life, so it's much easier. And obviously, with the wedding, she was a massive help.
"There's no question you can't ask, and no point you can raise, that she won't already know about - and have a better opinion about."
The Duke of Cambridge has also revealed the 85-year-old monarch has always made it clear to him and his brother Prince Harry to treat her as their grandmother first and the queen second.
And although she is happy to offer advice to him, Elizabeth encourages William to work things out for himself first.
He explained: "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 (...) It's very much the case that she won't necessarily force advice on you. She'll let you work it out for yourself. She's always there for a question or two, for whatever it is you might need ... But, just as she probably had to do, she feels that you have to work it out for yourself, that there are no set rules. You have to make it work. You have to do what you think is right."