Prince Charles has disappointed Prince Philip in the past.

Several reports have claimed that the Prince of Wales and Duke of Edinburgh don't share a great father-and-son relationship. A new documentary may support this claim.

In Channel 4's documentary "The Royal House of Windsor," Sir Max Hastings revealed that Prince Charles' decision to snub a state dinner hosted by the Chinese government in 1999 didn't sit well with Prince Philip. In addition, many deemed it to be an embarrassment to the Queen. "This move turned to be a source of considerable frustration and dismay to Prince Philip, who's led an intensely disciplined life, with which he's kept his mouth largely shut, under intolerable stresses and strains, and he's been this absolutely rock-like support," Hastings said (as quoted by Express).

In a letter written in 1978, Prince Charles informed his private secretary that he wanted to do things differently rather than adopt what the current monarchy does. This was reportedly met with disapproval from Prince Philip.

"The Queen and Prince Philip had very strong ideas about how you do monarchy and Prince Charles comes along and starts doing things very differently," royal author Catherine Mayer said. "His father in particular actively opposed him."

In related news, Prince Philip reportedly called Prince Charles "silly" in a letter to Princess Diana. According to the duke, he didn't expect Prince Charles to leave Princess Diana for Camilla Parker Bowles. He also admitted that he and the Queen didn't want to see them with other partners.

However, in a secret interview that Princess Diana made, she confessed that Prince Philip advised Prince Charles to get back with Camilla if their marriage doesn't work.

"My father-in-law said to my husband, 'If your marriage doesn't work out, you can always go back to her after five years,'" Princess Diana said in a 2017 Channel 4 special that utilized taped conversations between the Princess of Wales and her voice coach. "Which is exactly—I mean, for real I knew that it had happened after five—I knew something was happening before that but the fifth year I had confirmation."

Prince Philip and Prince Charles
Prince Charles disappointed Prince Philip for not doing this for the monarchy. Pictured: Prince Philip and Prince Charles listen to speeches before a statue of the Queen Elizabeth, The Queen Mother was unveiled on Oct. 27, 2016 in Poundbury, England. Getty Images/Justin Tallis