At last some cautious optimism after the royal gloom

This is the first time that Buckingham Palace has said anything officially about the King's condition since revealing his cancer diagnosis.

So it's a significant moment, breaking the silence with a positive message about his treatment and announcing, if not a complete return to good health, then at least the first green shoots of recovery.

There has been so much terrible news for the royals this year - the Princess of Wales as well as the King facing cancer - that this must feel like a badly-needed change.

Like the picture of the King and Queen in Buckingham Palace's gardens, there's a touch of summer after a long bleak winter.

The dramatic Buckingham Palace statement, which more or less came with its own drum roll, has created a much more optimistic mood.

King Charles is going to resume the type of big engagements that he's had to cancel all year.

Anyone who has gone on a royal visit will have seen how much encounters with the public cheer him up, he's often shaking hands and swapping jokes with those he meets. He does literally seem to want to be a hands-on monarch.

Such encounters with ill health can readjust people's views and priorities and it will be interesting to see how it will affect the King. He's a thoughtful and deeply spiritual figure, who will now have another type of adversity to consider.

It's not a coincidence that his first visit next week will be to a cancer treatment centre where, with plenty of personal shared experience now, he will show his support for staff and patients.

The latest news suggests the King is well enough to host a state visit too, with the Emperor and Empress of Japan arriving in late June - an event which would usually involve the full royal red carpet treatment. These are the soft power moments where the King, as head of state, plays a pivotal role.

The last state visit was by the South Korean president and it showed the King's willingness to be creative with diplomacy, including having the band outside Buckingham Palace play 'Gangnam Style'. That was only before Christmas but it seems like a lifetime ago in royal news.

Royal commentator Richard Palmer, who has followed Charles's visits for many years, thinks the King will be keen to get his reign back on course.

"The King got off to a tremendous start in the new reign, much better than many royal watchers expected, but his and Kate's health problems have knocked the monarchy off course. He is a workaholic so I'm sure he has missed public-facing duties," said Mr Palmer.

He'll now have a second chance to start his reign.

The timing of the announcement might also have headed off some difficult questions that would soon have been arriving about the King's recovery.

There are a number of big royal summer events approaching - such as the garden parties, Trooping the Colour and the D-Day commemorations - which the King would have been expected to attend. There were overseas trips anticipated for the autumn too.

Despite the latest mood music, there is still no certainty over whether he will be well enough to be at any of these events.

That it's not possible to say whether he will be at engagements only a few weeks away might be a salutary reminder that this is still an ongoing problem. There might be optimism, but it's cautious optimism.

It's understandable for medical matters to remain private, but when you scratch below the surface of the latest statement, there is still much that remains unclear and unknown.

The King's cancer treatment has not stopped and there is still no date set for its conclusion. As many families will have found, living with cancer means living with many uncertainties.

It isn't back to business as usual.

In terms of the statement issued by palace aides, the positive message will have got ahead of any speculation. It's set the narrative on a much more upbeat direction, with the King's doctors "very encouraged by the progress made so far", rather than a drip-drip of cancelled attendances.

The photograph of the King and Queen issued alongside has, as intended, sailed straight onto the newspaper front pages. It's a conscious message of cheerful reassurance.

It's very much a his-and-hers image, the royal couple sharing a moment. The Queen has been standing in for the King in a way that would never have been expected a few months ago.

Author and historian Sir Anthony Seldon says the photo is "intriguing" in how much it focuses on the Queen.

"Deliberately or not," he says the photo give the impression that the "rock in the marriage" is Queen Camilla.

"Whether or not he will lean on her even more on his return we will see," says Sir Anthony.