Prince William used to "push tissues" under the door when his mother Princess Diana was crying.
The late Princess - who passed away in 1997 after she was involved in a fatal car crash - was known for having a troubled marriage to Prince Charles, and it has now been claimed that her eldest son William, 35, used to help pass his mother tissues when he heard her crying.
Andrew Morton, who wrote the 1992 biography 'Diana: Her True Story', revealed the sad news when he claimed Diana's brood - which also includes 32-year-old Prince Harry - "knew" about "the unhappiness of their mother".
He said: "I think as the sons of the future queen they would want to know more about their mother. Both boys lived through what was going on on a daily basis. To the point where William was pushing tissues through the bathroom door when Diana was crying. They knew what was going on at that time. They don't need me to tell them about the unhappiness of their mother and the distance of their father."
And the author also stood up for Harry, after he recently slammed the decision to make him walk behind his mother's coffin at just 12 years old.
Speaking on UK television show 'Loose Women', Andrew added: "From what I can gather from what Prince Harry has to say about his life, including about walking behind his mother's coffin at the funeral, he's trying to come to terms with his own life - he's had counselling."
Prince Harry spoke negatively about the decision which saw him walk behind the coffin in a procession through London with his grandfather, Prince Philip, his uncle, Earl Spencer, his father, Prince Charles and his brother Prince William, who was 15 at the time.
He said: "My mother had just died, and I had to walk a long way behind her coffin, surrounded by thousands of people watching me while millions more did on television.
"I don't think any child should be asked to do that, under any circumstances. I don't think it would happen today."