The secret being kept from Prince George

Prince George has just celebrated his fifth birthday but he's still far too young to know the truth about his future, reveal his parents. Photo / Matt Porteous

Born in to a life of incredible privilege, there's something about what is yet to come for Prince George that his parents have decided is better left off his radar - for now.

According to a new book, George's parents, the Duke and Duchess of Cambridge, are keeping a pretty major piece of information from him, in order to protect their 5-year-old son and give him as normal an upbringing as possible.

Third in line to the British throne, behind his father, Prince William, and grandfather, Prince Charles, George is being kept in the dark about his position in the Royal Family and potential to become king.

Detailed in the book "Charles: The Heart of a King", author Catherine Mayer says William found the prospect of his future role burdensome and grappled with the magnitude of it as he grew up.

Prince George meeting former US President Barack Obama. Photo / Getty Images

Speaking to E! News back in 2015, she said William and Catherine intend to delay for as long as possible "that moment of realisation and give him normality before they thrust this on him."

William and his wife have often spoken of their "very normal" life as a family behind closed doors.

As a young man, William is said to have struggled with the notion of becoming king. Photo / Getty Images

"There'll be a time and a place to bring George up and understand how he fits in, in the world. We are very normal." he has said, adding that his three children, George, 5, Charlotte, 3 and newborn Louis, will grow up in a "real, living environment," rather than be kept out of society and behind palace walls.