Prince George recently turned 12 years old, and according to royal experts, one "morbid rule" is now expected to go into effect.

Royal protocol advises that George will no longer be allowed to fly with his father, Prince William. Heirs are required to fly separately to preserve the line of succession should an accident occur while they are traveling. William, 43, is heir to the throne.

"The Prince and Princess of Wales and their children are the future of the royal family," royal expert Richard Fitzwilliams told Fox News Digital. "Accidents do happen, and this seems like a sensible precaution which ought to be observed, as it was with King Charles and William during Queen Elizabeth's reign."

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"There are reports that the king and William, who is a pilot, disagree over this," Fitzwilliams shared. "But it should be necessary to point out that Harry is fifth in line to the throne... and only four working royals are under 70… The need for Prince George as second in line to the throne to fly separately from his father surely makes sense."

Fox News Digital reached out to Kensington Palace for comment.

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The king’s former pilot, Graham Laurie, previously confirmed on "A Right Royal Podcast" that he initially flew Charles, William, Harry and Princess Diana together, but that changed when William turned 12, Us Weekly reported.

"After that, he had to have a separate aircraft, and we could only fly all four together when they were young with the written permission of Her Majesty," said Laurie, as quoted by the outlet. "When William became 12, he would fly normally in a 125 from Northolt, and we would fly the 146 out with the other three on."

British broadcaster and photographer Helena Chard claimed to Fox News Digital that the king had made it known that he expected George to travel separately from his father. She noted that father and son will have to "adjust to the change."

"Traditional royal travel protocol expects a future heir to travel separately from their father, especially when 12 years old," Chard explained. "Direct heirs should not fly together. Previous generations left children at home with governesses when traveling. This, however, caused a lot of upset for the children. King Charles can vouch for this; he desperately missed his parents when they were away on tour."

Still, Chard said that it’s likely George and William will ease into the change.

"This important matter is being debated as it could impact the future of the monarchy," she claimed. "Travel arrangements for the heir to the throne are important at any age. And the Wales family have always traveled together… There are many rules, expectations and traditions that the royal family is expected to follow."

British royals expert Hilary Fordwich pointed out to Fox News Digital that the rule isn’t set in stone. However, she noted that it’s a travel protocol that monarchs have taken seriously over the years.

"Rules, such as not traveling by plane or car together, now that Prince George is 12, are unwritten but a tradition," she explained. "This ensures that the next in line and heir are not lost. It has, on occasion, been relaxed or bent. Now, with the king’s health issues, combined with his advanced age, it is considered extremely important to ensure Prince George’s safety."

"Prince William and Princess Catherine are adhering to many rules, especially those protecting the succession," Fordwich shared. "But to a certain extent, they’ve reinterpreted other rules, relaxing or even disregarding others, in an admirable attempt to become a more relatable modern family. Every royal generation has likewise updated traditions, thereby remaining relevant."

"The restrictions on William and George flying together are a decades-long edict to ensure continuity should one die in a travel accident," added royal expert Ian Pelham Turner.

"Whether this will change or be challenged by William in the future and break decades of tradition is not known," he said. "But these days, with the royal family, that is not uncommon."

Royal author Robert Jobson previously wrote in his biography, "Catherine, the Princess of Wales," that the king "raised concerns" with William over his helicopter use with his wife, Kate Middleton, and their three children. William had expressed a strong desire to fly with his entire family.

Not only did this reportedly spark a tense disagreement, but the king presented William, an experienced pilot, with "a formal document acknowledging the risks involved and taking full responsibility for his actions."

A spokesperson for Kensington Palace, which handles the offices of the Prince and Princess of Wales, didn’t immediately respond to Fox News Digital’s request for comment. A spokesperson for Buckingham Palace declined to comment.

"There have been several royals who have perished in plane crashes," Fordwich previously explained to Fox News Digital. "As a result, Queen Elizabeth II was particularly sensitive regarding who could and would be permitted to fly together. Rules were put in place years ago regarding the prohibition of royal heirs from flying together."

"Much of the royal protocol was insisted upon by the late Queen Elizabeth II," Chard pointed out.

Still, the Prince and Princess of Wales aren’t afraid to bend the rules on occasion, she said.

"[In the past], Prince George would have endured certain rites of passage," Chard explained. "However, the Prince and Princess of Wales do not agree with some of the old-fashioned traditions, such as the ‘blooding ritual,’ especially when these traditions are not etched in stone. This makes perfect sense as some expectations, especially trivial and old-fashioned etiquette, are no longer relevant in today's modern world."

"A few traditions that the Prince and Princess of Wales have broken tend to be fashion-related. I imagine not complying with some of the protocol is a much-welcomed shift."

"The royals are far more touchy-feely these days, selfies are occasionally permitted, especially by William," said Fitzwilliams. "The king is a hugger, and William and Catherine communicate by video. The succession to the throne is pivotal to the future of the monarchy, and the deep rift in the royal family underlines its importance. [Still], George should not fly in the same aircraft as his father."

Christopher Andersen, author of "The King," previously told Fox News Digital that once George turned 12, he and his father would mark the beginning of a lifestyle change after the "morbid rule" kicks in.

"Starting at age 12, heirs to the throne are required to take air trips separately to preserve the line of succession should an accident occur," said Andersen at the time.

"When William turned 12, he began flying in a separate royal jet apart from his father and brother Harry," he shared. "It's a morbid rule, but then again, when they turn 16, all senior royals are also asked to help plan their own funerals."

Fox News Digital's Ashley Hume contributed to this report.