Prince William and Prince Harry reportedly have another similar trait to their late mom, Princess Diana.

British journalist, writer and broadcaster Robert Jobson penned an article for Daily Mail in 2018 for King Charles' 70th birthday celebration. The event happened three days after the Duke and Duchess of Sussex tied the knot. Prince Harry marked the occasion with a speech, and he delivered a warm message for his dad.

Prince William missed the event because he was on official duty to commemorate the anniversary of the Manchester Arena terror attack.

Princess Diana, Prince William, Prince Harry
(Photo : JOHNNY EGGITT/AFP via Getty Images)
Princess Diana (L), Prince Harry, (C) and Prince William (R) gather for the commemorations of VJ Day, 19 August 1995, in London.

Jobson quoted an anonymous source close to the royals who claimed that the monarch still struggled to gauge his sons at the time due to their unpredictable moods.

"In that aspect of their nature, both princes are very much like their mother," the insider claimed.

Princess Diana
(Photo : TORSTEN BLACKWOOD/AFP via Getty Images)
Diana, Princess of Wales, smiles as she meets wellwishers outside St Vincent's Hospice in Sydney on November 2, 1996, her last official engagement in Australia.

A former courtier seemingly echoed the same sentiment regarding the royal siblings' temperament compared to their mom's.

"They both have quite extreme mood swings, just as Diana did," the courtier said. "She could be your best friend one minute and the next your worst enemy."

Prince Harry, Prince William
(Photo : Jane Barlow - WPA Pool/Getty Images)

Jobson acknowledged that the brothers had a complicated relationship with their dad, and it was understandable. The royal biographer claimed that the King was absent much through their childhood.

King Charles eventually sorted out his relationship with his two sons. However, Prince Harry severed his ties with his own family after he left the royals in 2020, dropped his Netflix docuseries "Harry & Meghan" and released his memoir "Spare," which contained detailed accounts of his physical rows with his big brother and sentiments about King Charles' parenting.

Meanwhile, Prince William and King Charles' relationship had reportedly improved.

Prince Harry, Prince William
(Photo : Ian Vogler-WPA Pool/Getty Images)

When Jennie Bond, royal commentator and former BBC journalist, appeared on TalkTV in December, she was asked about the tender moment between King Charles and Prince William during the former's coronation, and the royal expert claimed that the father and son had become closer after Prince Harry and Meghan Markle left.

Prince William and Prince Harry
(Photo : DOMINIC LIPINSKI/POOL/AFP via Getty Images)
Prince William and Prince Harry attend the unveiling of a statue of their mother, Princess Diana at The Sunken Garden in Kensington Palace, London on July 1, 2021,

"During the rehearsal, we saw William looking at his father, and I think, probably going through William's head was also, 'My goodness, this is my destiny too.' But he has this caring side, you can see that he cares about his father a great deal," Bond said. "They've become a lot closer since Harry and Meghan left."