Prince William and Prince Harry "don't mess" with their grandmother.
The young royals revealed that although they think of Queen Elizabeth simply as their granny, they are careful not to upset her.
Speaking in ABC special, Harry, 27, said: "Behind closed doors, she's our grandmother, it's as simple as that."
William, 29, added: "As I learned from growing up, you don't mess with your grandmother."
Harry has previously revealed Queen Elizabeth is hilarious and said she and Prince Philip are a great double act.
He said: "She is very funny, but I think she gets it from my grandfather. They are very funny together. My family is the same as any other family when it comes to humor behind closed doors, though I'd like to think I was funnier than my grandmother."
He also explained he is happy to perform royal duties when his grandmother asks him but his military career remains a priority.
Harry said: "I will help out with my grandmother whenever she needs me, but I have this job that does suck up a lot of my time, and that's the number one for me."
'The Real Queen By Her Own Royal Family' is due to air in the US on May 29.