Prince Harry and Meghan Markle should be cautious with their next move, according to a royal expert.

Tessa Dunlop, a British historian, writer and broadcaster, sat down for an interview with Us Weekly while promoting her new royal book "Elizabeth & Philip: A Story of Young Love, Marriage and Monarchy." During the chat, she warned Prince Harry and Meghan to be careful with the timing of their future plans and announcements after two members of the royal family -- King Charles and Kate Middleton -- were diagnosed with cancer.

Reports previously claimed that the Duke and Duchess of Sussex wanted to return to their royal duties despite criticizing the monarchy in the past.

"They deliberately criticize the monarchy [and then offer] themselves as an alternative to monarchy. So then, when the monarchy is in trouble, we do kind of make a comparison. Can Harry and Meghan really hold themselves off as the caring example now?" Dunlop said.

"They're certainly going to have to be careful of their timing with any releases so that it doesn't look opportunistic."

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Prince Harry, Meghan Markle, Catherine, Duchess of Cambridge, Kate Middleton
Prince Harry, Meghan Markle, Catherine, Duchess of Cambridge and Prince William, Duke of Cambridge (not pictured) attend the first annual Royal Foundation Forum held at Aviva on February 28, 2018 in London, England.
(Photo : Getty Images/Eddie Mulholland - WPA Pool)

She added that the pair based in Montecito should tread lightly on whatever they put out because "The big C -- it's kind of untouchable," and when it creeps on one's door, it "just reframes everything."

As for Prince Harry's feelings after learning that his sister-in-law has cancer too, Dunlop believes that he was in a difficult position, especially after all the things he shared about Middleton in his memoir "Spare."

"When you do discover that your sister-in-law has cancer and you've written stuff that can't be retracted, that's quite a painful place to be in," Dunlop added. "I'm not saying it isn't."

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Diamond Jubilee - Service Of Thanksgiving
LONDON, ENGLAND - JUNE 05: Catherine, Duchess of Cambridge and Prince Harry smile as the leave a Service Of Thanksgiving at St Paul's Cathedral on June 5, 2012 in London, England.
(Photo : Photo by Matt Cardy/Getty Images)
In his book, Prince Harry recounted an incident when Middleton allegedly "grimaced" after his wife borrowed the latter's lip gloss. He also claimed that the Princess of Wales had several complaints about how his bride-to-be planned their royal wedding and mentioned the duchesses' row over the bridesmaid dresses.

Prince Harry claimed that he had found Markle sobbing on the floor, overcome by stress and worry.Many hoped that Middleton's cancer diagnosis would end the feud between the Sussexes and the royal family. However, Prince William and Middleton allegedly have no plans to reconcile with Prince Harry and Markle after all the things they did since stepping away from their royal duties in 2020.

Prince Harry and Meghan Markle
Prince Harry, Duke of Sussex, and Meghan, Duchess of Sussex after attending the National Service of Thanksgiving at St Paul's Cathedral during the Queen's Platinum Jubilee celebrations on June 3, 2022 in London, England.
(Photo : Toby Melville - WPA Pool/Getty Images)