What King Charles' cancer diagnosis means for Prince William

LONDON -- There is never a good time to find out a parent has cancer. It's a particularly difficult moment for Prince William.

His father's cancer diagnosis comes as the heir to the British throne was already navigating a health scare at home. It was only last month that his wife Catherine had abdominal surgery that will sideline her for several months.

Little is known about the Princess of Wales' procedure, but her lengthy recovery signals a serious operation. With three young children to care for, William's diary was also cleared. His priority abundantly clear: Family comes first.

With Charles' candid disclosure, those plans are evolving. William is now unexpectedly needed to pick up some of his father's public-facing responsibilities, given he's the next-in-line. He's been thrust into a role that not too long ago Charles was doing for the late Queen Elizabeth II - stepping in as needed while the monarch was temporarily unavailable.

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The demands of being the immediate heir saw William make a partial return to royal duties on Wednesday after a three-week absence. He kicked things off by hosting an investiture ceremony at Windsor Castle. Dressed in his RAF uniform, he smiled warmly, charming guests while doling out honors on his father's behalf.

The prince has "an unwavering commitment to duty and service," a royal source told CNN, adding that "investitures are an important part of his royal role, celebrating people up and down the country doing incredible things for their communities."

Later, he attended a gala dinner in central London as the patron of the London Air Ambulance, where he publicly addressed the royal double health scare for the first time.

"I'd like to take this opportunity to say thank you, also, for the kind messages of support for Catherine and for my father, especially in recent days. It means a great deal to us all," William said.

He then quipped: "It's fair to say the past few weeks have had a rather 'medical' focus. So, I thought I'd come to an air ambulance function to get away from it all."

Beyond those two engagements, there is nothing else scheduled for him in the days ahead. That could partly be down to a school break next week but also because the 41-year-old royal is continuing to make his family his focus.

Charles, who flew to his Sandringham home after a blink-and-you-miss-it reunion with Prince Harry on Tuesday, is still handling state matters while going through his unspecified treatments. That will give William some flexibility as it means the prince appears not to be needed to pick up any constitutional business. But that will be something his staff are carefully coordinating with Buckingham Palace.

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While it could be some time before we next see him, the Prince of Wales will likely be called on to lead the family for the annual Commonwealth Day service - a staple celebration in the royal calendar that will be held at Westminster Abbey on March 11.

The developments this week will have been an eye-opener for William, with the future surely occupying some of his thoughts. The Prince of Wales has never been in a rush to be King. He knows a greater share of the royal burden falls on him with every passing year and has taken it on willingly. He's not shy about taking on the top job one day, but he has other things he wants to do first.

As William himself put it during a sit-down with the BBC in 2016, he thinks it's "important to grow into a particular role with the right characteristics and right qualities."

He has repeatedly said and shown that he wants to be a more present parent. With his public service, he has spent the last 17 months reinventing his version of the Prince of Wales role in a way that is noticeably different to his father's tenure.

William has narrowed in on key themes - his ambitious eco-prize and pioneering five-year plan to tackle homelessness - where he wants to bring measurable change. He's also seen his father's strong international relationships, and ramped up his diplomatic efforts by taking trips designed to build his own ties with Britain's allies and partners.

The King's diagnosis means William is now one of the most prominent faces of the clan - alongside Queen Camilla. As such, the demands on his time increase and he doesn't have as many working royals backing him up as he had once hoped to.

The other eight working family members are continuing their public engagements and CNN understands they could also pick up some additional duties on Charles' behalf if needed.

Queen Camilla, for example, has been undertaking a full program of public duties in recent weeks, with no sign of taking her foot off the gas. Meanwhile, Princess Anne - known for her no-fuss attitude and quietly steadfast service - already stepped in this week with an investitures ceremony on Tuesday.

William's challenge in the days and weeks ahead is how he uniquely balances his personal and professional commitments.

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