Just like his mother before him, King Charles has shown remarkable resilience this week – returning to his royal duties just days after being rushed to hospital due to complications with his on-going cancer treatment.

However, while the Royal Family continue to bravely endure what has been an incredibly tough few years for them – from Prince Harry and Meghan Markle’s departure in 2020, Prince Philip’s death in 2021, the late Queen’s death a year later and Kate Middleton andKing Charles’ cancer diagnoses last year – this latest hurdle is, for many, a sure sign that they still have huge hurdles to face.

And now a source says the King’s latest health scare has been ‘a reality check’ for Prince William, 42, and Kate Middleton, 43, who are on ‘high alert’ to be called up to rule.

The insider says, ‘King Charles’ latest health crisis has put Prince William and The Princess of Wales on high alert in case they’re called on to rule sooner than expected.

‘They’ve been hoping that he’ll beat this and have many more years on the throne, andthey’re certainly still praying that will be the case. But they can’t stick their heads in the sand and ignore the fact that this could change.

‘His hospitalisation last week has been a reality check. It was a reminder for the whole family that he is still very unwell and the fact is, as with any monarch, they have no control over when they’ll be called up to the throne.’

King Charles, 76, announced his diagnosis of an undisclosed type of cancer in February last year, which Buckingham Palace revealed had been discovered after an operation for an enlarged prostate.

Buckingham Palace has described last Thursday’s brief hospital stay as a ‘minor bump’ in the road. Side effects of cancer treatment are not rare or uncommon, but in some cases, can worsen over time.

Now the source says that, with Queen Camilla, 77, also said to be encouraging Charles to not over-do his work commitments, it could reach the stage where it is better for the monarch’s health to abdicate the throne to Prince William and Kate – although this event is very rare.

The insider says, ‘Whether Prince William and Kate Middleton ascend to the throne by an abdication due to King Charles’ failing health, or whether it comes through the tragic event of his passing, it’s something that is coming closer by the day. 

‘As much as William and Kate want to believe he will beat this, it goes without saying that they are ready and willing to do their duty. The royals have to run their lives somewhat like a business, so although they don’t want to contemplate losing Charles, they also have to prepare for it, and in that regard, they are ready.’

For the Royal Family, it’s always been essential that the Royal Protocol is in place – something even the likes of Prince George, who at just 11 is second in line to the throne, will be made aware of. 

Like the late Queen, whose death was announced to the Prime Minister and officials with the code, ‘London Bridge is down’, King Charles’ death will now take on the same message, after being updated from ‘Operation Menai Bridge’ following his mother’s passing. 

The source says, ‘It’s crucial that continuity be maintained when the changeover happens. William has been taking on more high-profile duties and he’s stepped in at key state functions to take the pressure off his father. 

‘He’s also getting the weekly government briefings alongside Charles so that everything is second nature when the time comes for him to be King.’ 

And while Kate – who is mum-of-three to Prince George, 11, Princess Charlotte, nine, and Prince Louis, six – is still recovering from her own cancer battle after revealing she was in remission in January, the source says she has also been preparing for her future role as Queen Consort.

They add, ‘Kate has been doing her part as well. As much as her work in early childhood development and mental health is a personal passion, it’s also being seen as a platform that can be carried forward when she’s Queen. 

‘They are very focused on what needs to be done to prepare. It’s something they’ve been working towards for years, but it’s all accelerated in recent months. 

‘Charles trusts them implicitly, he has no doubt that they will do a fantastic job when the time comes, and that vote of confidence means the world to William and Kate.’ 

However, the source makes it clear that the family are rallying around Charles – who is due to visit Italy next week – to support him to remain monarch for as long as he wishes and is able to. 

They add, ‘King Charles has shown remarkable strength and is still very keen to remain on the throne for as long as he can. 

‘William and Kate are doing all they can to help make that possible for him. Kate has been especially helpful in keeping his spirits up. She’s checking in on him daily and encouraging him.’ 

Now, while sources have said the King is ‘back to business as usual’, Prince William and Kate have continued to juggle their busy family life with building their own image as ‘modern royals’ and honing in on their passion projects. 

To mark Mother’s Day, the Wales’ released a poignant video celebrating Mother Nature to promote caring for the environment – an area that stems across both Kate’s work in early childhood and William’s with the annual Earthshot Prize. 

Now the source says this is all part of the couple’s plan to create a future monarchy that feels more relatable, especially to young people. 

The insider says, ‘They represent the monarchy’s future, and their public image needs to reflect the values that matter most to younger generations.’ 

And with last month marking a year since Kate’s shock diagnosis, the source says she and William – who described 2024 as the ‘hardest year’ of his life – are working as a team now more than ever.

They add, ‘It’s a daunting task, but they are up for it. William is immensely grateful to have Kate by his side, she’s smart and capable and such a steadying force for both him and his father. 

‘He’s thanking his lucky stars that she’s back to good health and ready to be his Queen.’