FILE PHOTO: (Clockwise) Prince Charles Prince William holding his son Prince George, Duchess Catherine and Queen Elizabeth. Picture: Bang Showbiz

Prince William shares a "special closeness" with his grandmother Queen Elizabeth, as she was the one who prepared him to become King in the future.

The 35-year-old royal is the second in line to the throne behind his father Prince Charles, and the 91-year-old monarch is said to have been training her grandson for the day he takes over as King since he was a teenager, by going through state papers with him.

Robert Lacey, historian and consultant to the hit Netflix series 'The Crown', told People magazine: "There has always been a special closeness between William and the Queen, and she has taken a particular interest in him. It's no secret that she and Charles have had a prickly relationship at times. When William became a teenager, she would have him at Windsor Castle and would open the state boxes and guide him through the papers. It was William's constitutional education."

The news comes after William - whose wife Catherine, Duchess of Cornwall, is expecting their third child - previously described the Queen as a "role model".

He said last year: "[She is] the best role model I could have. [She has] more of a soft influencing, modest kind of guidance. I don't think she believes too heavily in instruction. My grandmother takes more of a passive role in how she believes her role should be. She's above politics."

Meanwhile, although Prince William has been revealed in public surveys as being more popular than his 68-year-old father, it was revealed earlier this year that he won't be "elbowing him out the way" when it comes to taking over the throne. 

A source claimed: "Some people may question why William still won't do as much as Princess Anne but he is dead set on not queering his father's pitch. 

"He sees that Charles will probably be in his seventies before he becomes King and he doesn't want to be seen as elbowing his father out the way."