While the rest of her subjects call Queen Elizabeth II "Your majesty," her great-grandson knows her as "Gan-Gan."
The Duchess of Cambridge reveals that tidbit in a television documentary celebrating the queen's 90th birthday to be broadcast on Britain's ITV channel over Easter.
In her first solo interview since marrying Prince William in 2011, the former Kate Middleton says the queen is a doting great-grandmother to Prince George and Princess Charlotte and "she always leaves a little gift or something in their room when we go and stay."
"Our Queen at Ninety" also features interviews with the Prince of Wales, the Duchess of Cornwall and Prince Harry. The queen turns 90 on April 21, but her official party will take place in June with a celebration in London.