Prince Philip wanted Prince Charles to be tough.

According to royal biographer Penny Junor, there’s something in the Prince of Wales that the Duke of Edinburgh doesn’t like. This has something to do with Prince Charles being a weak man.

“The trouble is that the Prince of Wales is fundamentally a weak man, and that is what has incensed the Duke of Edinburgh over the years,” Junor wrote in her 2005 book “The Firm.”

“He wanted a son in his own image – a tough, abrasive, plain-talking, unemotional man’s man – but those qualities bypassed his first son and settled instead on his daughter.”

Junor pointed out Prince Charles’ generous heart and how he cares hugely about the underdog. The future king is passionate in making the world a better place. However, although Prince Charles is admirable in many ways, he has never been able to cope with confrontation and never been brave when it comes to making tough decisions because he gets others do it for him.

Prince Philip shares a warmer relationship with his second son, Prince Andrew. In fact, the 97-year-old royal calls the Duke of York “the boss.”

Prince Philip and Prince Andrew used to play mock bedtime boxing. One time, Prince Andrew’s boisterous spirit resulted in Prince Philip having a “black eye” on the night he was due to attend a movie premiere.

Queen Elizabeth II’s husband just made fun of it. When he stepped out of the car, he pointed to his black eye and ruefully said, “That was the boss.”

According to royal biographer Andrew Morton, Prince Philip and Queen Elizabeth II treated Prince Andrew differently from Prince Charles and Princess Anne. After welcoming their third baby, the Duke of Edinburgh and the Queen decided to not expose Prince Andrew to the public as much as his two older siblings because they realized that “excessive publicity had a harmful effect” on their children, particularly on Prince Charles who was by nature very shy.

Royal experts also believed that Prince Andrew is Queen Elizabeth II’s favorite son. The monarch was more hands-on to Prince Andrew compared to the Prince of Wales.

Prince Charles and Prince Philip
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