It comes after the monarch received treatment for an enlarged prostate only to be followed by a cancer diagnosis.
While the type of cancer has not been revealed, it has been announced that it is not prostate cancer.
Charles is said to remain wholly positive about his treatment and looks forward to returning to full public duty as soon as possible, though the episode has thrown William into the spotlight.
Now, one royal commentator has noted how he will have been thrown by the pace that events have unfolded, with a reality check about his future in tow.
GB News’s Mark Dolan asked royal commentator Pandora Forsyth whether the episode was “a wake-up call” and what William will now be thinking that his time on the throne “is coming”.
“I think it has been a complete shock for everybody,” Ms Forsyth said. “[Charles] is the oldest monarch we’ve ever had, so quite frankly, that fact that we’re now thinking about this not even two years into his reign is quite worrying.”
No further details are being shared on the stage of Charles’ cancer or a prognosis. The King informed both his sons personally about his diagnosis and William is said to be in regular contact with his father.
Harry, the Duke of Sussex, returned to the UK from the US for a short period this week after receiving the news. He is said to have spent around an hour with his father in a private meeting before jetting back to the States.
Shortly after his return, he appeared at the NFL Honours awards ceremony where he cracked jokes to a pleased crowd, though made no mention of his father or brother.
Questions are now being asked about the role other members of the Firm have in their positions as working royals.
Prince Edward is set to return to royal duties after a short break, as is Princess Anne. Meanwhile, Prince Harry and Prince Andrew are no longer called on as they are non-working royals.
The Prince of Wales was similarly taking a short break from public engagements while he helped his wife Catherine, Princess of Wales, as she recovered from abdominal surgery she had last month.
Ms Forsyth said there was little to no chance that Charles would take a step back from his duties as he enjoyed working so much and there was no sign that his doctors had advised him not to work.
She said: “He doesn’t work too hard, he loves his work, and he also understands what a privilege it is to be working in his position.
“He loves working with the charities and so does the Queen, it really gives him the opportunity to push [those causes] forward.”