Princess Diana reportedly urged Prince William and Prince Harry to not be like their grandfather, Prince Philip when they grow up.

According to royal biographer Ingrid Seward, Princess Diana and Prince Philip exchanged a few letters that eventually became too much for the late royal.

In one of the letters, the Duke of Edinburgh encouraged Princess Diana to reflect on why Prince Charles left her for Camilla Parker Bowles.

“Although the precise details of all the letters are not available, the substance of Philip’s missives was that Charles was wrong to have returned to Camilla, but that Diana, too, was wrong to have other lovers. Eventually, it was too much for Diana. Unable to take criticism of any sort, she decided she hated Philip (that is what she told me) and his mission failed,” Seward said.

Queen Elizabeth’s husband previously denied that he sent Princess Diana harsh letters. And the Princess of Wales’ former royal butler, Paul Burrell also came to the 99-year-old retired royal’s defense.

According to Burrell, Prince Philip did more to save Prince Charles and Princess Diana’s marriage than the heir to the throne himself.

Following Princess Diana’s death in 1997, her friend, Teddy Forstmann claimed that Princess Diana told him that she hated Prince Philip. Seward echoed Forstmann’s statement.

“When I saw the Princess at Kensington Palace shortly before her death, she told me the same, adding that she had warned her sons: Never, never shout at anyone the way Prince Philip does,” Seward said.

The royal expert also said that Prince Philip disliked Sarah Ferguson more than Princess Diana. In fact, the queen’s husband never shied away from criticizing Ferguson publicly.

“Philip became more and more irritated with Fergie and what he described as her ‘antics.’ He began to take every opportunity to criticize her, and disliked what he considered her informality with the staff. She became nervous in his presence, and when she tried to make polite conversation, he let his contempt be known. He also goaded Andrew, picking on him at every opportunity,” she said.

The mom of two reportedly found this insulting and it gave her the courage to admonish Prince Philip when he slammed Prince Andrew during one of their dinners.

Fergie reportedly confronted Prince Philip and told him that he couldn’t talk to the Duke of York that way.