Princess Diana and Sarah Ferguson
Princess Diana was jealous of Sarah Ferguson because she knew how to win the hearts of the royal family. Pictured: Prince Andrew, Ferguson, Lord Linley, Prince Edward, Prince Charles, Princess Diana, Queen Elizabeth II and Queen Mother outside her London Clarence House residence on Aug. 4, 1989. Getty Images/Johnny Eggitt

Princess Diana and Sarah Ferguson were still on speaking terms when the latter informed the former that she has plans to write a memoir.

According to a royal expert, the Princess of Wales told the Duchess of York that she’s supporting her 100 percent. But after Fergie’s memoir was released, Princess Diana became upset with her royal best friend.

While speaking with The Evening Standard, royal author Robert Jobson said that Princess Diana got upset with Fergie because she asked the royal to not write about her in her memoir. But Prince Andrew’s ex-wife talked about Princess Diana multiple times in the publication.

Royal author Katie Nicholl revealed that Ferguson made several attempts to make it up to Princess Diana, but the latter bore a grudge after reading the memoir. Jobson added that the two female royals could’ve actually repaired their relationship if only the Princess of Wales lived longer.

“[Princess Diana] could really hold a grudge,” Nicholl said.

The royal author’s statement coincided with what the Princess of Wales’ former royal butler, Paul Burrell, previously said about his boss.

The “I’m A Celebrity Get Me Out of Here” star said that Princess Diana didn’t have any problem cutting people off.

“I’ve been in similar situations where people said things about Princess Diana, and the way she dealt with it was by freezing them out. It looks as if Harry has taken a leaf out of his mother's book… Diana said: ‘Once someone burns the bridge of trust towards you it's very hard to repair it,’” Burrell said.

Meanwhile, Fergie recently said that she still misses Princess Diana to this day. During her interview with Harper’s Bazaar, the mom of two confirmed that she tried everything to win Princess Diana’s trust back but to no avail.

But just before Prince Charles’ ex-wife died, she called one of her friends and asked about Fergie. Princess Diana fondly called her fellow royal, “Red,” because she’s a redhead.