There is concern to be had whenever someone of such advanced years goes into hospital, but the Duke of Edinburgh has seen the inside of the King Edward VII hospital in central London a few times in recent years, and he has always come out smiling several days later.
And so, at the moment at least, there appears to be no undue alarm inside Buckingham Palace about the Duke’s health.
They haven’t said exactly what he is being treated for – other than feeling unwell at Windsor Castle yesterday – and royal sources are keen to highlight he was driven in, he wasn’t an emergency case and he walked through the doors of the hospital unaided.
It’s unusual for the Palace to rule out any medical condition, but given the extraordinary times we are living in, they have said that his condition is not related to Covid-19.
In fact, the Queen and her husband had their coronavirus jab a few weeks ago as they were in the second highest priority category because of their respective ages: she 94; he 99.
And it's because Prince Philip is just a few months away from his 100th birthday that this hospital admission cannot be taken too lightly, despite what the Palace aides are advising.
It is still the winter months, there is a pandemic sweeping the country, and older people are more vulnerable at this time of year to many viruses.
So the medics inside the private King Edward VII hospital will be keeping a very close watch on the man, who is the longest serving consort in British history.
The Duke has spent a lot of time with the Queen over the past year after being moved in March 2020 from Sandringham to Windsor.
He has been enjoying his well-earned retirement time at Wood Farm, a relatively small cottage complex on the Norfolk estate.
But as the coronavirus was brought into the United Kingdom at this time last year, the Queen was moved from Buckingham Palace and Philip from Sandringham.
Together at Windsor Castle, they have spent their time being looked after by a small coterie of staff, often referred to as HMS Bubble, which looks after the Queen and Duke on a strict rotation of isolation.
It was there they spent what aides called a “quiet Christmas” without the rest of the family that they would normally see during the festive period at Sandringham.
Prince Philip has made a career out of surprising those who might try to second-guess his recovery from treatment.
Many thought he would have to miss Harry and Meghan’s wedding in 2018 because, shortly beforehand, he was sent to hospital for a hip operation – a big deal for any person in their nineties.
But a few weeks after he was discharged, Prince Philip walked unaided to his seat at St George's Chapel to watch his grandson get married.
Other thought he might miss the big Christmas gathering in 2019 after being admitted to the same hospital for an undisclosed condition in mid-December.
Instead, he left on Christmas Eve and made his way to the family gathering in Norfolk.
So we await further news on his health. Unless there is a marked deterioration, we won’t get anything soon.
Buckingham Palace is always reluctant to issue a regular medical bulletin on any senior member of the Royal Family – who all, understandably, like to keep at least some things in their lives private.