Prince William will celebrate his 30th birthday next month

Prince William knows that his grandmother's boss.

The 29-year-old, who's 2nd-in-line to the throne behind his father Prince Charles, 63, knows he should respect Queen Elizabeth, who celebrates her Diamond Jubilee this year.

'As I learned from growing up, you don't mess with your grandmother,' says Wills.

And though she's the Queen of England, Wills' younger brother, Prince Harry, 27, doesn't treat his granny like an intimidating monarch.

'Behind closed doors, she's our grandmother,' Harry tells US chat show host Katie Couric in a rare interview.

'It's as simple as that.'

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Esme Riley