Kate's cancer diagnosis: Business as usual outside Windsor ...

At Windsor this morning, crowds lined the streets to watch the Irish Guards pipe and drum their way into the castle grounds to change duties with the Welsh guards.

It was business as usual.

The palace says constitutionally the same is true for the senior royals, even if there is a temporary changing of the guard.

The King is still holding audiences with dignitaries, but he has stepped back from public-facing engagements, and there is a sense of frailty in the royal household.

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Former press secretary to the late Queen, Ailsa Anderson, says: "This is not a crisis, it's a bump in the road."

But she added: "It's very, very difficult obviously, and unsettling, because this is an institution based on stability and continuity, and you have two key players who are going to be out of action for some time."

The late Queen had to step up her duties when her father was diagnosed with cancer in the late 1940s. The disease accelerated her accession to the throne when he died aged just 56.

She famously said: "I need to be seen to be believed."

How true that was of Princess Catherine - whose disappearance from the public eye sparked a frenzy of conspiracy theories.

And although she's addressed those with her sobering reality, she won't be back in the public gaze until medics say she's fit to go.

For now, she can expect public curiosity has been replaced with sympathy, but clearly there is a lot on Prince William's shoulders.

He will want to spend as much time as possible with Catherine and their three children, and will be with them at least for the Easter break.

But with his brother abroad and to some degree estranged, and his uncle Prince Andrew relieved of duties, there's a dwindling pool of royal big-hitters available to hold the fort.

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Constitutional expert Craig Prescott said: "There has been a slimming down.

"There has been more emphasis on a small number of royals. So when two are out of action, that is perhaps a bigger issue."

Queen Camilla has become a key player.

She delivered a speech written by the King on his behalf, on the Isle of Man this week, and next week she'll play his role at the Maundy Thursday service in Worcester; a key royal fixture.

The remaining support team, Princess Anne, and the Duke and Duchess of Edinburgh are likely to have more focus on them too.

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Even Prince Andrew was leading the family at a recent memorial service in Windsor when William needed to be with Catherine.

This isn't quite a crisis, but it is a test of resilience for the royals.

They hope this is only a temporary situation, but what we've learned in recent weeks is that while they crave privacy in illness, the public craves information.

Finding that balance is just one of many challenges ahead.